Great Lakes Water Levels and Temperatures

Weather and Climate

Great Lakes

This indicator measures water levels and surface water temperatures in the Great Lakes.

Figures

Figure 1. Water Levels of the Great Lakes, 1860-2023

Data source: NOAA, 2024⁸
Web update: June 2024

Figure 1

This figure displays how water levels in each of the Great Lakes have changed since 1860. For each year, the shaded band shows the range of monthly average water levels, and the line in the middle shows the annual average. The graph uses the 1981 to 2010 average as a baseline for depicting change. Choosing a different baseline period would not change the shape of the data over time. Lakes Michigan and Huron are shown together because they are connected at the same water level.

Show the data behind this figure

year	Lake Erie level	Lake Erie lower bound	Lake Erie upper bound	Lake Michigan-Huron level	Lake Michigan-Huron lower bound	Lake Michigan-Huron upper bound	Lake Ontario level	Lake Ontario lower bound	Lake Ontario upper bound	Lake Superior level	Lake Superior lower bound	Lake Superior upper bound
1860	1.23	0.59	1.93	2.89	2.15	3.34	0.75	0.40	1.68	0.14	-0.41	0.50
1861	1.29	0.05	2.03	2.88	2.04	3.57	1.36	0.27	2.30	0.18	-0.38	0.70
1862	1.39	0.70	2.14	2.82	2.38	3.22	1.38	0.40	2.66	-0.10	-0.61	0.27
1863	1.13	0.09	1.70	2.38	2.05	2.67	0.97	0.36	1.97	-0.48	-0.87	-0.09
1864	0.50	-0.20	1.36	1.77	0.97	2.22	0.74	-0.03	1.97	-0.68	-1.04	-0.35
1865	0.14	-0.86	0.76	1.48	0.75	2.15	0.71	-0.52	1.45	-0.42	-1.33	0.24
1866	0.27	-0.68	0.88	1.15	0.42	1.71	0.00	-0.78	0.63	-0.54	-1.50	0.01
1867	0.31	-0.68	1.27	1.58	0.79	2.27	0.63	-1.31	2.27	-0.28	-0.94	0.14
1868	-0.05	-1.26	1.00	1.10	0.53	1.69	-0.68	-1.80	0.36	-0.43	-1.27	-0.15
1869	0.34	-0.73	1.27	1.21	0.24	2.11	0.33	-0.95	1.15	-0.24	-1.33	0.54
1870	0.96	0.35	1.45	2.12	1.29	2.74	1.39	-0.03	2.79	-0.01	-0.68	0.73
1871	0.37	-0.64	1.04	2.04	0.65	2.88	-0.01	-1.28	0.95	-0.01	-1.23	0.57
1872	-0.58	-1.06	-0.05	0.91	0.30	1.50	-1.38	-1.83	-0.82	0.14	-0.74	0.87
1873	0.11	-1.15	0.96	1.52	0.33	2.20	-0.33	-1.90	0.79	0.70	0.04	1.36
1874	0.60	-0.54	1.15	1.92	1.28	2.33	0.42	-1.15	1.12	0.68	0.18	1.19
1875	-0.09	-0.94	0.58	1.68	1.08	2.17	-0.88	-1.77	-0.23	0.76	0.34	1.26
1876	1.29	-0.04	2.12	2.73	1.70	3.64	0.94	-0.85	2.20	1.16	0.27	2.01
1877	0.44	-0.05	0.95	2.43	2.14	2.75	-0.22	-0.92	0.40	0.52	0.18	0.83
1878	0.87	0.39	1.35	2.18	1.81	2.58	0.35	-0.65	0.86	-0.03	-0.48	0.41
1879	0.08	-0.67	0.58	1.31	0.98	1.57	0.06	-1.05	0.66	-0.49	-0.87	-0.15
1880	0.34	-0.36	0.89	1.47	0.96	2.17	-0.31	-1.05	0.46	-0.14	-1.17	0.54
1881	0.18	-0.81	0.93	1.86	1.14	2.25	-0.64	-1.44	0.13	0.31	-0.38	1.06
1882	1.06	-0.03	1.66	2.20	1.70	2.66	0.42	-0.52	1.41	0.24	-0.09	0.54
1883	0.87	-0.12	1.76	2.48	1.66	3.38	0.53	-0.85	1.87	-0.02	-0.35	0.31
1884	0.93	0.04	1.74	2.69	2.18	3.10	1.14	0.00	2.04	-0.15	-0.71	0.50
1885	0.83	-0.49	1.57	2.84	2.36	3.37	0.68	-0.55	1.45	0.14	-0.38	0.64
1886	0.93	0.22	1.50	3.07	2.41	3.72	1.45	0.30	2.50	-0.26	-0.61	0.01
1887	0.90	0.01	1.65	2.41	1.43	2.95	0.91	-0.39	2.04	-0.20	-0.61	0.18
1888	0.21	-0.42	0.84	1.77	1.23	2.35	-0.33	-0.85	0.20	0.21	-0.61	1.00
1889	-0.05	-0.66	0.73	1.26	0.69	1.79	-0.12	-0.98	0.66	0.07	-0.45	0.60
1890	0.64	-0.05	1.56	1.09	0.62	1.69	0.92	0.10	2.00	-0.05	-0.71	0.54
1891	-0.28	-1.22	0.32	0.52	-0.11	0.94	-0.03	-1.70	1.32	-0.48	-0.68	-0.25
1892	-0.28	-1.33	0.95	0.36	-0.15	1.02	-0.77	-1.67	0.17	-0.45	-0.94	-0.02
1893	-0.35	-1.27	0.79	0.54	-0.23	1.33	-0.21	-1.41	1.18	-0.09	-0.94	0.57
1894	-0.35	-0.88	0.41	0.74	0.21	1.45	-0.40	-1.60	0.63	0.58	-0.28	1.09
1895	-1.27	-1.74	-0.87	-0.11	-0.93	0.24	-1.90	-2.79	-1.18	0.62	0.01	1.16
1896	-1.04	-1.61	-0.43	-0.42	-0.86	0.06	-1.57	-2.39	-0.75	0.61	-0.05	1.13
1897	-0.48	-1.36	0.19	0.18	-0.59	0.89	-1.39	-2.36	-0.55	0.61	0.11	1.19
1898	-0.32	-0.93	0.36	0.33	-0.29	0.87	-0.83	-1.54	-0.06	0.16	-0.55	0.77
1899	-0.51	-1.12	0.10	0.34	-0.41	1.13	-0.99	-1.83	-0.13	0.70	-0.25	1.55
1900	-0.51	-1.10	0.01	0.35	-0.13	0.77	-0.96	-1.67	-0.19	0.79	0.14	1.55
1901	-1.07	-1.59	-0.56	0.61	0.12	1.14	-1.10	-1.87	-0.16	0.76	0.24	1.23
1902	-0.64	-1.84	0.27	0.25	-0.24	0.87	-0.84	-1.74	0.00	0.55	-0.02	0.93
1903	-0.09	-1.05	0.61	0.39	-0.23	0.86	-0.31	-1.37	0.50	0.80	0.01	1.46
1904	0.04	-1.16	1.04	0.87	-0.06	1.58	0.46	-1.47	1.71	0.70	0.18	1.23
1905	-0.32	-1.31	0.57	0.99	0.32	1.61	0.03	-0.88	0.79	0.73	0.04	1.32
1906	-0.22	-0.78	0.19	1.01	0.57	1.50	-0.14	-0.65	0.40	0.61	0.13	0.93
1907	0.27	-0.22	0.85	1.08	0.65	1.67	0.47	0.13	0.92	0.49	-0.09	1.13
1908	0.21	-1.05	1.04	0.99	0.26	1.79	1.10	-0.69	2.43	0.23	-0.41	0.87
1909	-0.32	-1.08	0.73	0.47	-0.07	1.15	-0.07	-1.01	1.12	-0.10	-0.74	0.37
1910	-0.58	-1.31	0.14	0.16	-0.42	0.56	-0.52	-1.31	0.27	-0.25	-0.61	-0.02
1911	-1.04	-1.46	-0.57	-0.39	-0.62	0.02	-1.14	-1.70	-0.52	-0.59	-1.50	0.18
1912	-0.48	-1.43	0.15	0.07	-0.75	0.70	-0.06	-1.44	1.15	0.06	-0.61	0.64
1913	0.44	-0.37	1.52	0.71	0.09	1.33	0.81	-0.29	1.84	0.28	-0.51	1.00
1914	-0.35	-1.11	0.51	0.25	-0.30	0.70	-0.14	-1.37	0.76	0.33	-0.22	0.77
1915	-0.84	-1.41	-0.23	-0.33	-0.56	0.03	-1.09	-1.47	-0.72	0.03	-0.74	0.77
1916	-0.22	-1.01	0.78	0.38	-0.69	1.15	0.17	-1.15	1.74	1.04	0.08	1.75
1917	0.21	-1.19	1.31	1.13	0.43	1.91	0.23	-1.11	1.28	0.42	0.08	0.70
1918	-0.97	-1.63	-0.64	1.43	0.84	2.02	0.17	-0.32	0.92	-0.09	-0.71	0.34
1919	-0.45	-1.40	0.57	0.94	0.31	1.53	0.46	-0.49	1.77	0.14	-0.25	0.41
1920	-1.33	-2.51	-0.61	0.54	0.05	1.10	-0.82	-1.24	-0.52	0.24	-0.28	0.80
1921	-0.94	-1.53	-0.18	0.11	-0.38	0.61	-0.49	-1.44	0.46	0.01	-0.58	0.47
1922	-1.27	-2.22	-0.38	-0.05	-0.71	0.71	-0.52	-1.64	0.66	-0.12	-0.87	0.54
1923	-1.83	-2.48	-1.23	-0.64	-1.13	-0.11	-1.24	-1.90	-0.32	-0.45	-0.81	-0.12
1924	-1.56	-2.35	-0.78	-0.87	-1.36	-0.25	-0.85	-1.70	0.00	-0.74	-1.14	-0.25
1925	-2.38	-2.78	-1.92	-1.76	-2.35	-1.39	-1.41	-2.03	-0.65	-1.07	-1.43	-0.64
1926	-2.22	-3.27	-1.53	-1.89	-2.61	-1.39	-1.37	-2.19	-0.85	-1.37	-2.09	-0.55
1927	-1.63	-2.28	-1.01	-1.00	-1.76	-0.38	-0.69	-1.37	-0.16	-0.12	-0.94	0.54
1928	-1.20	-1.79	-0.51	-0.05	-1.16	0.67	-0.06	-0.59	0.50	0.37	-0.51	1.26
1929	-0.02	-1.30	1.06	1.46	0.57	2.38	0.86	-0.49	2.20	0.47	0.21	0.70
1930	-0.15	-1.53	0.73	0.64	-0.48	1.26	0.86	-0.98	1.87	0.27	-0.25	0.73
1931	-2.02	-2.48	-1.50	-1.10	-1.69	-0.80	-1.51	-2.29	-0.82	-0.09	-0.64	0.24
1932	-1.89	-2.71	-1.37	-1.69	-2.21	-1.33	-1.05	-1.93	-0.10	0.24	-0.25	0.73
1933	-2.09	-3.07	-1.10	-1.92	-2.41	-1.23	-1.77	-2.82	-0.82	0.27	-0.38	0.70
1934	-3.24	-3.70	-2.84	-2.25	-2.58	-1.92	-2.62	-3.54	-1.74	0.47	-0.05	0.83
1935	-2.97	-3.73	-2.35	-1.85	-2.35	-1.33	-2.69	-3.31	-1.90	0.50	0.14	0.96
1936	-2.71	-3.73	-2.02	-1.69	-2.15	-1.26	-2.16	-3.41	-0.95	0.34	-0.09	0.77
1937	-1.63	-2.58	-0.61	-1.76	-2.15	-1.30	-1.05	-2.23	-0.16	0.31	-0.28	0.83
1938	-1.56	-2.61	-0.91	-1.03	-2.28	-0.34	-0.98	-1.80	-0.26	0.67	-0.02	1.23
1939	-1.53	-2.22	-0.84	-0.61	-1.26	0.02	-1.08	-2.10	-0.06	0.67	0.14	1.29
1940	-1.69	-2.65	-0.97	-1.03	-1.39	-0.61	-1.28	-2.42	-0.23	0.08	-0.64	0.64
1941	-2.02	-2.65	-1.56	-1.10	-1.30	-0.87	-1.34	-2.23	-0.65	0.27	-0.58	1.16
1942	-1.43	-2.68	-0.71	-0.41	-1.10	0.21	-0.98	-2.23	-0.10	0.60	0.08	0.96
1943	-0.28	-1.37	0.83	0.57	-0.67	1.53	1.02	-0.59	2.56	0.83	0.27	1.46
1944	-0.74	-1.43	0.18	0.48	-0.02	0.87	0.10	-0.92	0.99	0.50	-0.41	1.39
1945	-0.41	-1.83	0.47	0.38	-0.41	1.07	0.79	-0.95	1.71	0.60	0.08	1.13
1946	-0.58	-1.50	0.24	0.48	-0.44	1.03	0.56	-0.52	1.25	0.54	0.01	0.90
1947	-0.25	-1.66	1.13	0.38	-0.67	1.16	1.15	-0.46	2.76	0.64	-0.12	1.29
1948	-0.32	-1.30	0.64	0.25	-0.64	0.90	0.86	-0.32	2.10	0.11	-0.48	0.57
1949	-1.14	-2.15	-0.55	-0.80	-1.69	-0.25	-0.26	-1.57	0.79	0.27	-0.45	0.93
1950	-0.58	-1.37	0.14	-0.64	-1.62	-0.05	0.23	-0.98	1.15	0.90	-0.09	1.65
1951	0.01	-0.71	0.73	0.94	-0.38	1.62	1.41	0.23	2.63	1.13	0.50	1.59
1952	0.67	-0.45	1.46	2.05	1.53	2.71	1.81	0.53	3.09	0.90	0.34	1.65
1953	0.04	-0.84	0.80	1.56	0.94	2.18	0.66	-0.55	1.71	0.41	-0.25	1.19
1954	-0.09	-1.07	0.57	1.23	0.48	1.72	0.53	-0.65	1.64	0.18	-0.51	0.87
1955	0.11	-1.04	0.83	0.87	-0.25	1.49	1.09	0.30	2.20	-0.05	-0.64	0.44
1956	-0.64	-1.89	0.27	-0.05	-0.54	0.54	0.33	-0.72	1.58	-0.12	-0.64	0.41
1957	-0.91	-1.56	-0.02	-0.64	-0.97	-0.08	-0.62	-1.47	0.20	-0.12	-0.78	0.41
1958	-1.66	-2.38	-1.17	-1.26	-2.12	-1.00	-1.28	-2.06	-0.72	-0.18	-0.71	0.37
1959	-1.53	-2.48	-0.74	-1.46	-2.31	-1.07	-1.11	-2.16	0.13	0.14	-0.58	0.93
1960	-0.74	-1.46	0.08	0.08	-1.03	1.03	-0.36	-1.28	1.05	0.21	-0.45	0.67
1961	-0.71	-1.69	0.27	-0.25	-0.71	0.02	-0.69	-1.93	0.59	-0.15	-0.61	0.21
1962	-1.33	-1.76	-0.87	-0.77	-1.59	-0.28	-0.59	-1.80	0.36	-0.18	-0.68	0.37
1963	-1.92	-2.74	-1.27	-1.76	-2.44	-1.30	-0.52	-1.67	0.79	-0.18	-0.81	0.27
1964	-2.32	-3.01	-1.60	-2.54	-2.87	-2.21	-1.74	-3.15	-0.46	-0.05	-0.87	0.60
1965	-1.99	-2.81	-1.40	-1.76	-2.81	-1.16	-1.37	-3.24	-0.36	-0.05	-0.64	0.31
1966	-1.37	-1.92	-0.78	-0.97	-1.46	-0.51	-0.42	-1.05	0.30	0.14	-0.32	0.60
1967	-0.84	-1.43	-0.32	-0.51	-1.30	0.15	0.13	-0.95	1.09	0.08	-0.48	0.57
1968	-0.38	-0.94	0.14	-0.02	-0.61	0.48	-0.06	-0.95	0.86	0.44	-0.71	1.42
1969	0.24	-0.74	1.23	0.80	-0.02	1.62	-0.23	-1.24	1.09	0.50	-0.02	0.77
1970	-0.18	-0.78	0.37	0.74	0.25	1.13	-0.42	-1.31	0.56	0.31	-0.58	0.96
1971	-0.02	-0.55	0.54	1.13	0.54	1.66	-0.32	-1.28	0.66	0.73	0.27	1.13
1972	0.60	-0.38	1.13	1.43	0.64	2.02	0.40	-0.92	1.71	0.64	0.21	1.16
1973	1.39	0.47	2.18	2.18	1.62	2.77	1.28	-0.62	2.99	0.80	0.01	1.46
1974	1.23	0.37	1.98	2.08	1.49	2.84	0.82	-0.95	2.53	0.87	0.11	1.42
1975	1.00	0.41	1.42	1.69	1.20	2.28	-0.03	-0.85	0.92	0.77	0.34	1.09
1976	0.83	-0.55	1.59	1.46	0.18	2.28	0.73	-0.92	2.37	0.41	-0.38	0.90
1977	-0.05	-1.07	0.60	0.15	-0.25	0.38	-0.19	-1.24	0.27	0.04	-0.84	0.96
1978	0.18	-0.78	1.06	0.44	-0.08	0.84	0.33	-1.31	1.64	0.27	-0.18	0.83
1979	0.24	-0.91	0.87	1.10	0.08	1.79	0.07	-0.78	1.12	0.44	-0.48	1.06
1980	0.67	-0.18	1.26	1.13	0.64	1.56	0.00	-0.92	1.05	0.27	-0.09	0.64
1981	0.27	-0.61	0.93	0.80	0.34	1.20	-0.10	-1.01	0.63	0.01	-0.45	0.50
1982	0.34	-0.25	1.06	0.48	-0.02	0.77	-0.23	-0.95	0.82	0.21	-0.74	1.03
1983	0.67	0.14	1.26	1.23	0.67	1.85	0.00	-0.95	1.15	0.70	0.37	0.93
1984	0.67	0.14	1.26	1.46	0.80	1.98	0.27	-1.08	1.64	0.60	0.11	1.00
1985	1.36	0.44	2.18	2.21	1.33	2.61	0.20	-0.62	1.18	1.03	0.18	1.82
1986	1.91	1.19	2.37	2.74	2.15	3.43	1.09	0.27	1.71	1.23	0.83	1.59
1987	1.16	0.14	1.78	1.69	0.74	2.38	0.10	-1.24	1.28	0.37	0.04	0.73
1988	-0.18	-1.01	0.47	0.34	-0.11	0.80	-0.46	-1.18	0.33	-0.12	-0.61	0.34
1989	-0.28	-1.07	0.67	-0.18	-0.90	0.38	-0.19	-1.41	1.32	0.14	-0.28	0.57
1990	-0.09	-1.14	0.37	-0.34	-1.00	0.18	-0.06	-0.92	1.05	-0.32	-0.91	0.11
1991	0.04	-0.97	0.73	0.05	-0.48	0.67	0.17	-1.51	1.55	-0.05	-0.71	0.34
1992	0.14	-0.78	0.64	0.08	-0.31	0.28	0.04	-1.24	0.95	0.14	-0.45	0.60
1993	0.60	-0.25	1.23	0.80	0.08	1.49	0.73	-0.98	2.60	0.31	-0.38	0.87
1994	0.18	-0.48	0.83	0.74	0.34	1.20	-0.19	-1.05	0.92	0.27	-0.25	0.77
1995	-0.12	-0.81	0.44	0.25	-0.15	0.61	-0.26	-0.92	0.30	-0.05	-0.55	0.44
1996	0.18	-0.94	0.96	0.64	-0.28	1.26	0.17	-0.65	1.35	0.64	-0.18	1.39
1997	1.32	0.50	2.28	1.72	1.07	2.41	0.46	-0.75	1.68	0.80	0.41	1.19
1998	0.77	-0.97	1.82	0.87	-0.31	1.49	0.30	-1.74	1.97	-0.12	-0.55	0.18
1999	-0.71	-1.50	-0.12	-0.71	-1.53	-0.18	-0.82	-1.64	-0.03	-0.32	-0.97	0.37
2000	-1.07	-1.86	-0.18	-1.56	-2.12	-1.07	-0.13	-1.21	1.45	-0.58	-0.97	-0.09
2001	-1.33	-1.86	-0.74	-1.66	-2.25	-1.30	-0.39	-1.15	0.56	-0.51	-1.46	0.11
2002	-0.84	-1.66	0.04	-1.10	-1.79	-0.41	-0.10	-1.64	1.68	-0.25	-0.81	0.27
2003	-1.14	-1.92	-0.45	-1.85	-2.38	-1.36	-0.36	-1.74	0.99	-0.55	-1.07	-0.22
2004	-0.64	-1.53	0.14	-1.13	-2.02	-0.28	0.10	-1.05	1.05	-0.18	-0.94	0.37
2005	-0.48	-1.56	0.27	-1.20	-1.89	-0.80	-0.03	-0.88	0.95	-0.09	-0.45	0.21
2006	-0.58	-1.14	-0.15	-1.43	-1.89	-1.03	0.04	-0.62	0.53	-0.58	-1.23	-0.15
2007	-0.58	-1.69	0.11	-1.69	-2.54	-1.23	-0.23	-1.67	0.76	-1.23	-1.86	-0.58
2008	-0.51	-1.30	0.24	-1.49	-2.48	-0.71	0.20	-1.01	1.58	-0.48	-1.27	0.21
2009	-0.22	-0.97	0.47	-0.64	-1.46	-0.05	0.17	-1.11	1.22	-0.32	-0.87	0.21
2010	-0.84	-1.50	-0.02	-1.13	-1.95	-0.64	-0.49	-1.05	0.50	-0.71	-0.94	-0.45
2011	-0.25	-1.86	0.87	-1.36	-2.21	-0.64	-0.06	-1.34	1.68	-0.87	-1.60	-0.25
2012	-0.61	-1.63	0.24	-1.76	-2.77	-1.26	-0.39	-1.77	0.56	-0.84	-1.40	-0.18
2013	-0.84	-1.63	0.11	-1.82	-2.90	-1.20	-0.26	-1.44	1.05	-0.45	-1.50	0.41
2014	-0.35	-1.23	0.27	-0.51	-1.66	0.28	-0.16	-1.18	1.15	0.50	-0.41	1.16
2015	0.01	-1.07	1.39	0.44	0.08	0.90	-0.26	-1.34	1.28	0.70	0.21	1.09
2016	0.31	-0.48	1.09	0.80	0.18	1.26	-0.06	-1.18	0.95	0.73	0.34	1.13
2017	0.83	-0.09	1.69	1.03	0.05	1.79	1.15	-0.65	3.25	0.90	0.11	1.49
2018	1.13	0.11	1.88	1.36	0.90	1.72	0.27	-0.65	1.45	0.87	0.37	1.36
2019	1.72	0.96	2.70	2.25	1.16	3.00	1.45	0.04	3.58	1.29	0.70	1.72
2020	1.88	1.09	2.57	2.81	2.25	3.26	0.69	-0.72	1.77	1.13	0.70	1.49
2021	1.16	0.83	1.62	1.56	0.84	2.02	-0.32	-1.08	0.10	0.41	-0.09	0.67
2022	0.54	-0.38	1.19	0.64	0.05	1.16	-0.03	-1.37	1.15	0.31	-0.64	0.96
2023	0.54	-0.18	1.09	0.34	-0.15	0.80	0.27	-1.08	1.81	0.64	0.04	1.06

Figure 2

Figure 2. Surface Water Temperatures of the Great Lakes, 1995-2023

Data source: NOAA, 2024⁹
Web update: June 2024

Annual averages (CSV) Daily averages (CSV) EPA source data (CSV)

Figure 3

Figure 4

This figure shows the average surface water temperatures in each of the Great Lakes, as measured by satellites. The graphs on the left show annual averages for the full time period, while the graphs on the right show how average daily temperatures have changed between two time periods for comparison: 2014–2023 versus 1995–2004.

Note: on this page, the annual averages are in the first chart and the daily comparison is in the second, below it.

Show the data behind this figure

Annual averages:

year	Lake Erie	Lake Huron	Lake Michigan	Lake Ontario	Lake Superior
1995	51.71	47.14	49.10	49.83	42.68
1996	50.48	45.07	46.05	47.65	39.90
1997	50.44	45.69	47.14	48.41	41.33
1998	54.25	49.41	51.64	51.74	46.34
1999	52.93	48.98	50.51	51.45	44.38
2000	52.12	47.90	49.86	49.89	44.41
2001	51.86	47.21	48.68	49.40	42.77
2002	52.35	48.68	50.24	51.36	43.78
2003	50.78	46.14	47.68	48.13	42.21
2004	52.21	47.24	48.71	49.68	42.74
2005	52.98	48.96	50.80	51.37	45.23
2006	52.62	48.70	50.13	51.22	45.96
2007	52.95	48.17	50.13	50.66	43.84
2008	51.41	47.39	48.46	49.83	43.31
2009	51.64	46.81	47.95	49.30	42.27
2010	53.05	49.30	50.95	51.49	45.94
2011	52.71	48.08	49.46	51.13	44.28
2012	54.91	50.57	52.34	53.68	47.11
2013	52.15	48.39	49.67	51.33	43.52
2014	51.08	45.87	46.33	48.51	40.74
2015	52.42	47.64	48.64	49.51	43.18
2016	54.78	50.52	52.24	53.20	46.47
2017	53.50	49.24	50.74	51.98	44.45
2018	52.82	47.80	49.77	51.08	42.57
2019	52.21	46.79	48.40	49.63	42.89
2020	53.78	49.00	50.47	52.32	44.10
2021	54.41	50.29	51.80	53.02	46.65
2022	52.92	48.24	49.60	51.81	42.30
2023	53.63	49.61	50.96	52.55	44.55

Figure 5

Daily averages by period:

Julian day	Lake Erie, 1995-2004	Lake Erie, 2014-2023	Lake Huron, 1995-2004	Lake Huron, 2014-2023	Lake Michigan, 1995-2004	Lake Michigan, 2014-2023	Lake Ontario, 1995-2004	Lake Ontario, 2014-2023	Lake Superior, 1995-2004	Lake Superior, 2014-2023
1	36.83	38.06	37.54	38.52	38.71	39.43	38.94	40.24	36.58	37.72
2	36.63	37.91	37.38	38.38	38.53	39.30	38.78	40.14	36.51	37.54
3	36.50	37.71	37.26	38.21	38.41	39.18	38.67	40.01	36.41	37.38
4	36.31	37.54	37.17	38.06	38.49	39.16	38.70	39.99	36.39	37.36
5	36.14	37.39	36.93	37.92	38.23	38.99	38.27	39.73	36.21	37.26
6	35.84	37.11	36.57	37.71	37.99	38.76	38.05	39.62	36.09	37.18
7	35.66	36.82	36.42	37.51	37.92	38.64	37.92	39.36	36.05	37.05
8	35.55	36.58	36.30	37.30	37.87	38.44	37.83	39.20	35.99	36.96
9	35.17	36.40	36.20	37.20	37.80	38.40	37.72	39.16	35.90	36.92
10	35.02	36.17	36.09	37.11	37.65	38.31	37.66	38.99	35.81	36.82
11	34.95	35.95	36.07	36.89	37.60	38.16	37.90	38.86	35.93	36.67
12	34.89	35.88	35.97	36.80	37.49	38.05	37.78	38.83	35.84	36.55
13	34.62	35.73	35.77	36.70	37.26	37.91	37.60	38.76	35.75	36.47
14	34.40	35.60	35.69	36.59	37.08	37.80	37.46	38.59	35.68	36.41
15	34.23	35.47	35.62	36.52	36.96	37.76	37.40	38.47	35.63	36.30
16	33.86	35.23	35.31	36.35	36.83	37.67	37.26	38.38	35.47	36.24
17	33.81	35.11	35.21	36.26	36.78	37.54	37.10	38.31	35.43	36.19
18	33.76	35.01	35.10	36.19	36.66	37.44	37.04	38.26	35.38	36.15
19	33.70	34.76	34.98	36.06	36.53	37.39	36.91	38.13	35.38	36.04
20	33.34	34.61	34.89	35.90	36.38	37.28	36.83	38.00	35.30	35.94
21	33.29	34.48	34.78	35.72	36.26	37.19	36.74	37.77	35.19	35.85
22	33.18	34.42	34.86	35.61	36.13	37.11	36.71	37.59	35.16	35.76
23	33.14	34.34	34.47	35.54	35.90	37.00	36.41	37.58	34.88	35.68
24	33.14	34.27	34.36	35.44	35.85	36.91	36.27	37.52	34.77	35.60
25	33.14	34.16	34.33	35.40	35.78	36.83	36.16	37.46	34.66	35.56
26	33.11	34.06	34.28	35.29	35.69	36.74	36.03	37.36	34.54	35.43
27	33.12	33.98	34.24	35.24	35.66	36.69	35.90	37.26	34.46	35.38
28	33.11	33.88	34.23	35.11	35.60	36.47	35.85	37.14	34.41	35.22
29	33.09	33.77	34.25	35.02	35.59	36.34	35.89	37.04	34.40	35.07
30	33.06	33.63	34.13	34.89	35.50	36.28	35.80	36.94	34.23	34.98
31	32.82	33.56	34.05	34.79	35.43	36.11	35.76	36.72	34.19	34.79
32	32.73	33.63	34.03	34.91	35.37	36.15	35.77	36.85	34.14	34.77
33	32.72	33.64	34.02	34.82	35.32	36.18	35.78	36.89	34.10	34.71
34	32.71	33.70	33.92	34.78	35.24	36.08	35.75	36.91	34.05	34.65
35	32.71	33.51	33.83	34.62	35.18	35.96	35.73	36.89	34.04	34.53
36	32.71	33.43	33.89	34.51	35.21	35.90	35.80	36.73	34.21	34.42
37	32.95	33.39	33.86	34.46	35.10	35.84	35.77	36.60	34.15	34.38
38	32.76	33.34	33.81	34.33	35.11	35.75	35.60	36.22	34.08	34.34
39	32.76	33.32	33.70	34.34	35.08	35.69	35.47	36.19	33.99	34.26
40	32.76	33.28	33.65	34.32	35.02	35.66	35.37	36.37	33.90	34.20
41	32.73	33.30	33.57	34.24	35.04	35.61	35.21	36.31	33.84	34.14
42	32.69	33.33	33.54	34.17	35.08	35.51	35.04	36.22	33.80	34.04
43	32.66	33.33	33.48	34.09	35.11	35.46	35.00	36.14	33.71	33.98
44	32.62	33.16	33.43	33.96	34.96	35.36	34.82	35.98	33.64	33.89
45	32.62	33.08	33.40	33.82	34.89	35.30	34.68	35.92	33.55	33.81
46	32.64	33.06	33.41	33.86	34.80	35.28	34.60	35.94	33.51	33.76
47	32.66	33.10	33.40	33.85	34.71	35.28	34.62	36.01	33.47	33.74
48	32.68	33.11	33.38	33.83	34.66	35.31	34.87	35.95	33.42	33.72
49	32.72	33.12	33.37	33.84	34.63	35.27	34.82	35.94	33.40	33.70
50	32.76	33.22	33.34	33.81	34.68	35.30	34.86	35.96	33.35	33.67
51	32.74	33.23	33.32	33.75	34.72	35.35	34.85	35.98	33.34	33.66
52	32.76	33.25	33.25	33.81	34.78	35.41	34.89	36.05	33.34	33.67
53	32.77	33.33	33.24	33.86	34.79	35.37	34.90	36.11	33.34	33.63
54	32.78	33.41	33.24	33.82	34.84	35.36	34.96	36.12	33.40	33.61
55	32.84	33.40	33.22	33.76	34.85	35.35	35.03	36.12	33.38	33.59
56	32.89	33.42	33.19	33.78	34.80	35.28	35.03	36.06	33.38	33.58
57	32.98	33.51	33.19	33.79	34.83	35.28	35.19	35.91	33.35	33.58
58	32.99	33.54	33.16	33.80	34.87	35.30	35.22	35.91	33.25	33.61
59	33.00	33.55	33.15	33.78	34.97	35.25	35.19	35.86	33.24	33.57
60	32.97	33.60	33.17	33.72	34.86	35.17	35.20	35.61	33.23	33.52
61	32.95	33.59	33.21	33.69	34.81	35.12	35.19	35.63	33.26	33.46
62	32.88	33.63	33.19	33.65	34.80	35.11	35.22	35.68	33.29	33.43
63	32.87	33.65	33.21	33.63	34.76	35.07	35.22	35.71	33.35	33.42
64	32.96	33.66	33.22	33.63	34.74	35.10	35.20	35.76	33.31	33.45
65	32.97	33.74	33.24	33.68	34.71	35.18	35.13	35.79	33.26	33.48
66	32.96	33.84	33.18	33.69	34.73	35.29	35.12	35.80	33.31	33.51
67	33.17	34.07	33.13	33.74	34.67	35.32	35.12	35.82	33.18	33.55
68	33.20	34.21	33.13	33.77	34.56	35.31	34.98	35.80	33.13	33.57
69	33.20	34.29	33.12	33.78	34.52	35.48	34.85	35.99	33.15	33.61
70	33.16	34.34	33.08	33.88	34.53	35.48	34.78	36.09	33.15	33.63
71	33.28	34.42	33.11	33.86	34.61	35.48	34.83	36.09	33.20	33.63
72	33.23	34.48	33.14	33.88	34.70	35.52	34.92	36.12	33.23	33.68
73	33.27	34.52	33.13	33.88	34.73	35.56	34.98	36.16	33.23	33.68
74	33.33	34.60	33.14	33.88	34.77	35.53	34.92	36.18	33.24	33.68
75	33.39	34.73	33.16	33.96	34.72	35.59	34.90	36.20	33.24	33.67
76	33.37	34.77	33.15	33.94	34.77	35.63	34.88	36.18	33.16	33.69
77	33.32	34.84	33.15	34.04	34.83	35.71	34.87	36.22	33.17	33.72
78	33.52	34.89	33.30	33.99	34.88	35.71	34.97	36.24	33.13	33.70
79	33.57	34.96	33.30	34.07	34.90	35.74	35.11	36.24	33.17	33.69
80	33.61	34.99	33.35	34.09	34.92	35.53	35.14	36.18	33.21	33.72
81	33.83	35.17	33.36	34.13	35.01	35.55	35.15	36.22	33.27	33.74
82	34.03	35.36	33.48	34.20	35.13	35.76	35.22	36.41	33.36	33.79
83	34.10	35.61	33.52	34.26	35.16	35.83	35.28	36.51	33.42	33.82
84	34.22	35.78	33.50	34.31	35.20	35.85	35.45	36.58	33.42	33.81
85	34.34	35.92	33.58	34.37	35.27	35.89	35.46	36.61	33.41	33.87
86	34.47	36.06	33.46	34.40	35.28	35.92	35.54	36.66	33.41	33.89
87	34.59	36.23	33.55	34.45	35.32	35.96	35.62	36.72	33.37	33.90
88	34.75	36.42	33.55	34.49	35.41	36.02	35.68	36.80	33.37	33.92
89	34.94	36.59	33.60	34.58	35.49	36.10	35.78	36.89	33.42	33.93
90	35.10	36.81	33.66	34.63	35.49	36.17	35.87	36.96	33.42	33.97
91	35.52	36.92	33.69	34.70	35.58	36.22	35.84	37.00	33.43	34.02
92	35.73	37.03	33.70	34.74	35.60	36.29	35.86	37.06	33.43	34.06
93	35.98	37.16	33.75	34.77	35.68	36.39	35.90	37.09	33.51	34.10
94	36.14	37.37	33.84	34.82	35.67	36.48	35.93	37.14	33.55	34.16
95	36.28	37.56	33.88	34.94	35.68	36.57	35.97	37.21	33.64	34.22
96	36.54	37.86	33.95	35.02	35.95	36.67	35.90	37.34	33.76	34.26
97	36.96	38.16	34.01	35.20	36.04	36.80	35.84	37.49	33.79	34.29
98	37.34	38.43	34.05	35.34	36.06	36.87	35.90	37.64	33.72	34.33
99	37.48	38.62	34.18	35.45	36.09	36.92	36.16	37.73	33.76	34.35
100	37.43	38.78	34.18	35.52	36.13	37.02	36.34	37.83	33.71	34.45
101	37.48	39.06	34.14	35.63	36.15	37.16	36.44	37.92	33.79	34.55
102	37.75	39.49	34.36	35.83	36.27	37.39	36.51	38.22	33.89	34.76
103	38.36	39.89	34.50	36.03	36.28	37.52	36.76	38.41	33.86	34.85
104	38.54	40.15	34.67	36.18	36.25	37.60	36.95	38.51	33.84	34.98
105	38.70	40.42	34.78	36.27	36.35	37.68	36.87	38.58	33.97	35.01
106	38.95	40.76	35.02	36.32	36.57	37.78	37.03	38.69	34.07	35.02
107	39.17	40.96	35.04	36.37	36.63	37.91	37.23	38.76	33.95	35.00
108	39.45	41.12	35.13	36.44	36.70	38.00	37.25	38.85	34.14	34.96
109	39.74	41.27	35.20	36.50	36.91	38.09	37.26	38.95	34.20	35.01
110	40.18	41.59	35.43	36.58	37.11	38.15	37.44	39.03	34.35	35.08
111	40.58	41.73	35.53	36.64	37.26	38.19	37.56	39.12	34.42	35.09
112	40.92	41.95	35.80	36.78	37.32	38.27	37.78	39.24	34.36	35.19
113	41.32	42.27	35.95	36.92	37.48	38.33	38.01	39.32	34.38	35.23
114	41.60	42.57	36.07	36.96	37.78	38.40	38.13	39.41	34.61	35.23
115	41.99	42.96	36.18	37.03	38.00	38.55	38.02	39.58	34.90	35.25
116	42.36	43.11	36.58	37.10	38.22	38.63	38.31	39.72	34.74	35.31
117	42.77	43.20	36.51	37.29	38.37	38.73	38.52	39.84	34.66	35.38
118	43.01	43.42	36.66	37.53	38.53	38.86	38.69	39.95	34.76	35.44
119	43.23	43.65	36.91	37.70	38.96	38.98	38.72	40.02	34.88	35.52
120	44.05	43.96	37.28	37.91	39.12	39.17	39.23	40.15	35.15	35.69
121	44.60	44.39	37.48	38.15	39.25	39.42	39.84	40.34	35.03	35.84
122	45.02	44.90	37.56	38.33	39.43	39.58	40.08	40.61	34.99	35.94
123	45.49	45.35	37.85	38.49	39.67	39.73	40.34	40.90	35.22	35.95
124	45.99	45.78	38.32	38.64	39.90	39.88	40.52	41.13	35.42	36.01
125	46.79	46.18	38.40	38.82	40.07	40.05	40.86	41.33	35.54	36.13
126	47.31	46.64	38.70	39.02	40.09	40.27	41.18	41.59	35.71	36.22
127	47.82	47.15	38.82	39.25	40.27	40.57	41.44	41.84	35.76	36.38
128	48.02	47.73	39.04	39.41	40.51	40.80	41.45	42.11	35.88	36.48
129	48.10	48.16	39.21	39.55	40.68	40.97	41.69	42.37	35.99	36.50
130	48.55	48.45	39.52	39.67	40.96	41.18	41.88	42.58	35.99	36.57
131	48.75	48.94	39.57	39.89	41.01	41.46	42.02	42.75	35.99	36.74
132	49.04	49.39	39.68	40.20	41.32	41.74	42.18	43.08	36.23	36.94
133	49.55	49.78	39.95	40.53	41.63	42.01	42.37	43.51	36.31	37.11
134	50.05	50.13	40.27	40.86	42.01	42.26	42.77	43.97	36.40	37.20
135	50.60	50.49	40.59	41.12	42.15	42.54	43.49	44.33	36.57	37.24
136	50.75	50.87	40.77	41.36	42.33	42.82	43.71	44.72	36.77	37.33
137	51.01	51.23	41.01	41.67	42.59	43.10	43.89	45.18	36.78	37.43
138	51.68	51.70	41.48	41.95	43.13	43.35	44.21	45.44	36.97	37.59
139	52.17	52.09	41.90	42.12	43.50	43.58	44.46	45.63	37.00	37.76
140	52.39	52.49	42.19	42.34	43.55	43.89	44.76	45.78	37.12	37.91
141	52.63	52.98	42.27	42.70	43.68	44.29	44.81	46.18	37.16	38.12
142	52.81	53.65	42.16	43.12	43.70	44.85	44.75	46.65	37.28	38.36
143	53.23	54.40	42.52	43.68	43.88	45.46	44.89	47.32	37.39	38.71
144	53.25	55.23	42.77	44.22	44.17	46.08	45.20	48.03	37.61	38.99
145	53.30	56.19	43.03	44.75	44.46	46.63	45.35	48.65	37.59	39.18
146	53.51	57.35	43.14	45.35	44.56	47.26	45.67	49.61	37.73	39.32
147	54.06	58.37	43.41	46.07	45.03	47.81	46.18	50.84	38.15	39.44
148	54.45	58.98	43.89	46.64	45.52	48.24	46.98	51.64	38.06	39.52
149	55.10	59.25	44.20	47.04	45.78	48.63	47.43	52.00	38.16	39.62
150	55.62	59.47	44.50	47.35	45.95	48.97	47.87	52.16	38.35	39.67
151	55.85	59.60	44.69	47.61	46.30	49.39	47.92	52.33	38.52	39.58
152	56.19	59.76	45.00	47.70	46.86	49.58	48.08	52.56	38.78	39.51
153	56.61	59.97	45.17	47.86	47.10	49.80	48.42	52.71	39.10	39.61
154	56.82	60.35	45.33	48.23	47.25	50.14	48.60	53.07	39.03	39.82
155	56.98	60.54	45.71	48.67	47.63	50.59	48.88	53.36	39.21	40.03
156	57.46	60.66	46.32	49.12	48.23	50.95	49.49	53.67	39.38	40.27
157	58.18	60.94	46.99	49.41	48.97	51.18	50.42	53.92	39.52	40.46
158	59.18	61.36	47.60	49.84	49.45	51.57	51.60	54.18	39.71	40.69
159	59.60	61.74	48.06	50.33	49.96	52.02	52.42	54.52	40.04	40.90
160	60.38	62.09	48.82	50.68	50.73	52.44	52.97	54.81	40.20	41.12
161	61.52	62.32	49.52	50.93	51.37	52.84	53.76	55.05	40.31	41.37
162	61.98	62.62	50.27	51.04	51.83	53.10	54.54	55.37	40.51	41.50
163	62.31	63.01	50.70	51.14	51.91	53.33	55.32	55.75	40.67	41.55
164	62.63	63.53	51.23	51.38	52.34	53.54	55.96	56.37	40.78	41.61
165	63.11	63.82	51.49	51.60	52.66	53.83	56.30	56.64	40.98	41.80
166	63.48	64.21	52.10	51.99	53.21	54.25	56.69	56.96	41.40	42.15
167	63.92	64.76	52.37	52.55	53.39	54.72	56.94	57.62	41.57	42.54
168	64.23	65.34	52.85	53.23	54.01	55.24	57.26	58.55	41.87	42.88
169	64.75	65.84	53.40	53.90	55.04	55.76	57.64	59.55	42.37	43.10
170	65.00	66.20	53.77	54.48	55.57	56.26	58.45	60.09	42.70	43.33
171	65.38	66.58	54.21	55.13	56.52	56.84	59.35	60.56	42.91	43.62
172	65.90	66.85	54.66	55.56	56.84	57.24	60.00	61.01	43.12	43.66
173	66.25	67.17	55.17	55.91	56.99	57.62	60.50	61.36	43.42	43.80
174	67.10	67.39	56.37	56.34	58.06	58.09	61.02	61.77	43.93	44.09
175	67.91	67.63	57.26	56.89	59.05	58.56	61.44	62.39	44.47	44.33
176	68.86	67.87	58.09	57.32	59.59	58.88	62.46	63.01	44.73	44.47
177	68.79	68.24	58.18	57.70	59.49	59.17	63.45	63.58	44.86	44.73
178	68.54	68.82	58.10	58.09	59.94	59.69	63.25	64.14	45.03	45.20
179	68.97	69.43	58.69	58.56	60.93	60.34	63.55	64.70	45.38	45.70
180	69.45	69.81	59.08	59.29	61.20	61.35	63.92	65.12	45.81	46.17
181	69.69	70.21	59.51	59.90	61.76	61.91	64.33	65.67	46.07	46.53
182	69.79	70.58	59.41	60.52	61.59	62.27	64.36	66.17	46.02	46.89
183	69.88	70.95	59.13	61.12	61.61	62.66	64.05	66.67	46.32	47.28
184	70.35	71.40	59.62	61.80	61.97	63.42	64.31	67.07	46.53	47.85
185	70.39	72.00	59.63	62.59	61.93	64.34	64.69	67.61	46.51	48.27
186	70.37	72.47	59.44	63.14	61.72	64.89	64.59	68.24	46.91	48.49
187	70.39	72.67	59.59	63.14	62.06	65.06	64.30	68.59	47.35	48.59
188	70.56	72.63	60.00	62.99	62.64	65.01	64.39	68.69	47.83	48.73
189	70.69	72.58	60.25	63.01	62.90	65.18	64.28	68.67	48.37	49.04
190	70.54	72.72	60.38	63.35	63.19	65.54	64.43	68.75	48.53	49.45
191	70.42	73.02	60.30	63.86	63.30	65.89	64.48	69.10	48.76	49.93
192	70.44	73.21	60.67	64.20	63.49	66.09	64.66	69.45	49.74	50.31
193	70.70	73.25	61.39	64.31	64.20	66.44	64.85	69.66	50.71	50.61
194	71.28	73.39	62.40	64.43	65.07	66.71	65.75	69.78	51.32	50.86
195	72.16	73.48	63.40	64.49	65.59	66.82	66.71	69.78	51.65	51.14
196	72.87	73.50	63.75	64.66	65.98	66.95	67.22	69.75	51.86	51.47
197	72.89	73.50	63.98	64.93	66.54	67.13	67.35	69.95	52.30	51.75
198	73.00	73.62	64.20	65.28	66.89	67.43	67.96	70.16	52.77	52.23
199	72.92	73.85	64.33	65.70	67.16	67.75	68.24	70.38	52.85	52.82
200	73.10	74.20	64.27	66.06	67.16	68.01	68.31	70.70	53.27	53.17
201	73.35	74.46	64.40	66.19	67.33	68.17	68.20	71.02	53.97	53.35
202	73.29	74.56	64.72	66.24	67.65	68.24	68.39	71.11	54.56	53.60
203	73.31	74.63	65.21	66.34	68.02	68.43	68.83	71.17	54.91	53.92
204	73.40	74.69	65.44	66.41	67.97	68.60	69.12	71.18	54.95	54.35
205	73.44	74.65	65.49	66.52	67.91	68.78	69.35	71.10	55.04	54.84
206	73.34	74.74	65.80	66.80	68.26	69.01	69.39	71.14	55.42	55.38
207	73.41	74.95	65.68	67.19	68.41	69.25	69.63	71.37	55.83	55.98
208	73.40	75.11	65.79	67.45	68.53	69.44	69.61	71.61	56.20	56.49
209	73.49	75.14	65.99	67.60	68.66	69.49	69.56	71.75	56.45	56.64
210	73.59	75.07	66.05	67.60	68.73	69.53	69.57	71.78	56.63	56.66
211	73.59	75.02	66.55	67.62	69.15	69.65	69.85	71.75	57.26	56.87
212	73.97	75.06	67.13	67.76	69.53	69.79	70.32	71.84	57.69	57.23
213	74.28	75.15	67.27	68.01	69.61	69.96	70.80	72.09	57.97	57.63
214	74.36	75.25	67.22	68.26	69.60	70.19	70.88	72.31	58.20	58.04
215	74.57	75.33	67.52	68.42	69.90	70.37	71.09	72.43	59.03	58.37
216	74.89	75.41	67.88	68.49	70.03	70.38	71.78	72.55	59.49	58.57
217	74.88	75.46	67.90	68.49	69.99	70.41	71.80	72.63	59.61	58.74
218	74.53	75.44	67.88	68.48	70.01	70.48	71.64	72.65	59.85	58.96
219	74.63	75.35	67.98	68.48	70.35	70.55	71.46	72.61	60.35	59.35
220	74.79	75.25	68.24	68.57	70.54	70.64	71.60	72.61	60.30	59.84
221	74.80	75.25	68.31	68.75	70.39	70.78	71.77	72.73	60.17	60.27
222	74.72	75.31	68.15	68.89	70.16	70.91	71.85	72.83	59.99	60.52
223	74.72	75.35	68.20	68.93	70.21	70.91	71.76	72.84	60.05	60.58
224	74.75	75.31	68.19	68.91	70.12	70.83	71.92	72.81	60.14	60.61
225	74.66	75.27	68.27	68.88	70.02	70.83	72.01	72.76	60.18	60.79
226	74.72	75.25	68.26	68.93	70.02	70.85	72.03	72.70	60.30	61.08
227	74.65	75.16	68.18	69.07	70.22	70.88	72.12	72.65	60.31	61.33
228	74.58	75.10	68.12	69.19	70.01	70.96	72.35	72.62	60.15	61.47
229	74.46	75.05	67.98	69.26	69.74	71.00	72.13	72.57	59.73	61.53
230	74.27	74.98	67.83	69.22	69.58	71.02	71.89	72.44	59.36	61.55
231	74.00	74.98	67.72	69.24	69.56	71.08	71.37	72.33	59.37	61.62
232	73.91	75.05	67.79	69.31	69.48	71.06	71.29	72.38	59.59	61.61
233	73.73	75.09	67.57	69.29	69.42	70.85	71.40	72.50	59.51	61.44
234	73.61	75.02	67.27	69.14	69.39	70.63	71.18	72.39	59.65	61.33
235	73.54	74.95	67.22	68.98	69.54	70.57	71.06	72.20	59.94	61.37
236	73.38	74.82	67.23	68.85	69.52	70.51	70.98	72.10	60.16	61.35
237	73.12	74.78	67.16	68.75	69.60	70.34	70.79	72.15	60.46	61.20
238	73.34	74.75	67.50	68.58	69.78	70.08	70.84	72.19	60.72	60.97
239	73.67	74.64	67.48	68.37	69.95	69.93	70.72	72.11	60.71	60.81
240	73.60	74.56	67.30	68.16	69.89	69.82	70.58	72.01	60.52	60.62
241	73.44	74.58	67.13	67.94	69.80	69.70	70.34	71.94	60.44	60.42
242	73.26	74.47	66.95	67.70	69.54	69.58	70.28	71.79	60.37	60.30
243	73.13	74.31	66.81	67.58	69.34	69.47	70.38	71.62	60.27	60.36
244	72.99	74.20	66.76	67.55	69.44	69.38	70.15	71.50	60.42	60.44
245	73.09	74.11	66.71	67.52	69.42	69.29	70.12	71.45	60.45	60.42
246	72.95	74.07	66.74	67.46	69.46	69.19	69.86	71.45	60.32	60.38
247	72.96	74.12	66.71	67.40	69.38	69.04	69.89	71.53	60.40	60.25
248	72.92	74.16	66.92	67.29	69.48	68.87	69.92	71.58	60.36	60.03
249	72.81	74.06	66.90	67.14	69.32	68.72	69.74	71.51	60.28	59.84
250	72.56	73.89	66.67	66.94	68.94	68.51	69.54	71.34	60.01	59.69
251	72.23	73.66	66.61	66.74	68.61	68.25	69.35	71.04	59.74	59.50
252	71.89	73.26	66.43	66.49	68.46	67.98	69.08	70.63	59.67	59.32
253	71.63	72.82	66.33	66.23	68.22	67.68	68.68	70.20	59.46	59.09
254	71.34	72.43	65.92	65.89	67.84	67.31	68.33	69.77	59.32	58.72
255	71.26	71.97	65.80	65.55	67.76	66.93	68.09	69.27	59.20	58.49
256	71.01	71.61	65.51	65.27	67.34	66.63	68.03	68.91	58.96	58.33
257	70.90	71.39	65.31	65.09	67.00	66.48	67.74	68.75	58.62	58.16
258	70.76	71.27	65.00	65.06	66.51	66.47	67.58	68.70	58.32	58.09
259	70.43	71.26	64.66	65.12	65.99	66.57	67.30	68.67	57.83	58.08
260	69.95	71.31	64.29	65.18	65.50	66.61	66.97	68.68	57.66	57.98
261	69.58	71.28	64.18	65.10	65.14	66.51	66.69	68.62	57.44	57.84
262	69.29	71.19	63.89	64.95	64.82	66.39	66.35	68.48	57.15	57.84
263	69.12	71.13	63.62	64.93	64.52	66.34	65.89	68.32	56.73	57.79
264	68.65	71.05	63.33	64.93	64.34	66.30	65.42	68.20	56.53	57.51
265	68.22	70.80	62.89	64.74	63.94	66.08	64.94	68.00	56.20	57.26
266	68.00	70.38	62.47	64.43	63.44	65.81	64.62	67.59	55.80	57.33
267	67.50	70.14	62.00	64.27	62.86	65.65	64.39	67.38	55.47	57.29
268	67.04	69.91	61.74	64.07	62.50	65.50	64.01	67.29	55.16	57.04
269	66.69	69.66	61.37	63.83	62.18	65.27	63.64	67.11	54.84	56.73
270	66.59	69.33	61.00	63.53	61.81	64.93	63.40	66.84	54.64	56.42
271	66.16	68.93	60.73	63.13	61.48	64.52	63.35	66.45	54.25	56.13
272	65.89	68.61	60.32	62.76	61.13	64.15	62.91	66.12	54.02	55.82
273	65.53	68.23	59.92	62.44	60.84	63.88	62.60	65.69	53.79	55.59
274	65.17	67.84	59.56	62.12	60.61	63.57	62.03	65.22	53.52	55.48
275	65.06	67.41	59.21	61.74	60.29	63.18	61.80	64.71	53.12	55.37
276	64.63	67.02	58.74	61.40	59.85	62.80	61.17	64.17	52.74	55.22
277	64.15	66.68	58.27	61.06	59.41	62.36	60.67	63.65	52.30	54.96
278	63.74	66.35	57.80	60.71	59.10	61.98	60.28	63.28	51.92	54.69
279	63.40	66.08	57.33	60.42	58.70	61.69	59.76	63.05	51.58	54.40
280	62.99	65.86	56.90	60.21	58.33	61.34	59.31	62.79	51.24	54.05
281	62.77	65.64	56.64	60.00	58.04	60.97	58.84	62.49	51.01	53.66
282	62.56	65.34	56.44	59.69	57.70	60.62	58.52	62.17	50.75	53.24
283	62.26	65.01	56.26	59.31	57.56	60.34	58.25	61.78	50.61	52.91
284	62.16	64.64	56.17	58.94	57.47	60.02	58.14	61.38	50.48	52.64
285	62.01	64.24	55.97	58.60	57.34	59.63	57.89	60.94	50.27	52.40
286	61.97	63.80	55.73	58.14	56.92	59.14	57.80	60.44	49.97	52.07
287	61.71	63.33	55.44	57.66	56.56	58.58	57.59	60.00	49.70	51.73
288	61.29	62.85	55.07	57.21	56.27	58.11	57.19	59.53	49.42	51.39
289	60.84	62.34	54.69	56.68	56.02	57.61	56.81	59.07	49.09	51.04
290	60.48	61.79	54.34	56.12	55.64	57.12	56.39	58.52	48.80	50.73
291	60.21	61.27	54.07	55.68	55.35	56.77	55.96	57.96	48.57	50.51
292	59.75	60.91	53.76	55.39	55.07	56.47	55.55	57.63	48.28	50.32
293	59.37	60.64	53.42	55.13	54.71	56.12	55.35	57.34	48.03	50.13
294	58.91	60.35	53.01	54.90	54.36	55.82	55.00	57.06	47.78	49.93
295	58.44	60.00	52.59	54.64	54.05	55.52	54.44	56.73	47.57	49.64
296	58.04	59.71	52.23	54.38	53.75	55.19	54.00	56.41	47.35	49.40
297	57.64	59.52	51.93	54.14	53.48	54.92	53.46	56.27	47.14	49.09
298	57.26	59.24	51.64	53.79	53.13	54.58	53.09	56.02	46.91	48.68
299	56.98	58.87	51.45	53.42	52.94	54.31	52.79	55.69	46.78	48.45
300	56.59	58.51	51.30	53.06	52.71	54.12	52.55	55.32	46.63	48.27
301	56.07	58.17	51.01	52.77	52.44	53.86	52.26	55.00	46.51	48.09
302	55.64	57.71	50.82	52.45	52.21	53.48	52.03	54.61	46.36	47.83
303	55.70	57.26	50.65	52.12	51.89	53.14	51.93	54.13	46.17	47.63
304	55.39	56.87	50.53	51.83	51.65	52.78	51.63	53.64	46.01	47.40
305	55.10	56.48	50.31	51.56	51.40	52.37	51.41	53.26	45.89	47.18
306	54.69	55.98	50.02	51.23	51.07	52.05	51.03	52.84	45.60	46.88
307	54.29	55.61	49.70	51.01	50.73	51.81	50.57	52.43	45.32	46.70
308	53.96	55.32	49.43	50.84	50.48	51.61	50.29	52.13	45.07	46.52
309	53.59	55.10	49.19	50.66	50.31	51.33	50.02	51.91	44.81	46.32
310	53.25	54.91	48.91	50.43	50.22	51.02	49.67	51.69	44.66	46.05
311	53.00	54.62	48.70	50.16	49.96	50.73	49.30	51.45	44.57	45.85
312	52.72	54.31	48.49	49.93	49.58	50.53	49.00	51.24	44.39	45.71
313	52.35	54.05	48.17	49.71	49.27	50.33	48.75	51.06	44.26	45.48
314	52.02	53.77	47.87	49.43	48.95	50.10	48.47	50.78	44.12	45.28
315	51.70	53.48	47.60	49.13	48.61	49.80	48.27	50.52	43.96	45.08
316	51.40	53.18	47.38	48.85	48.29	49.45	48.08	50.23	43.78	44.81
317	51.04	52.80	47.20	48.57	48.01	49.08	47.83	49.85	43.64	44.49
318	50.61	52.29	46.98	48.24	47.75	48.77	47.59	49.43	43.52	44.15
319	50.14	51.88	46.77	48.02	47.51	48.45	47.40	49.06	43.38	44.00
320	49.76	51.44	46.53	47.74	47.29	48.12	47.23	48.81	43.22	43.83
321	49.45	50.87	46.29	47.42	47.09	47.70	47.08	48.50	43.02	43.58
322	49.14	50.28	46.08	47.07	46.86	47.32	46.93	48.13	42.83	43.37
323	48.82	49.72	45.89	46.65	46.69	47.02	46.75	47.69	42.64	43.09
324	48.53	49.29	45.74	46.21	46.52	46.71	46.57	47.27	42.50	42.69
325	48.25	48.93	45.58	45.99	46.32	46.51	46.39	46.92	42.33	42.55
326	47.98	48.46	45.38	45.71	46.16	46.25	46.18	46.62	42.14	42.36
327	47.74	48.03	45.17	45.43	45.94	46.06	46.02	46.36	41.89	42.21
328	47.47	47.72	44.93	45.20	45.67	45.90	45.86	46.24	41.62	42.06
329	47.12	47.48	44.70	44.93	45.46	45.68	45.65	46.16	41.41	41.87
330	46.83	47.20	44.48	44.72	45.24	45.45	45.45	46.03	41.27	41.68
331	46.57	46.87	44.26	44.47	45.08	45.24	45.24	45.82	41.14	41.56
332	46.27	46.64	44.05	44.32	44.92	45.03	45.00	45.56	41.00	41.44
333	45.86	46.37	43.84	44.16	44.71	44.81	44.77	45.33	40.87	41.32
334	45.52	46.11	43.64	44.00	44.54	44.61	44.64	45.18	40.74	41.23
335	45.18	45.90	43.41	43.83	44.33	44.42	44.52	45.04	40.64	41.07
336	44.93	45.67	43.17	43.66	44.18	44.23	44.25	44.86	40.52	40.92
337	44.64	45.39	42.82	43.52	43.88	44.08	44.07	44.63	40.41	40.85
338	44.45	45.10	42.74	43.38	43.71	43.97	43.96	44.43	40.32	40.77
339	44.30	44.85	42.52	43.26	43.55	43.85	43.76	44.25	40.25	40.73
340	44.11	44.63	42.39	43.11	43.42	43.71	43.69	44.11	40.13	40.66
341	43.84	44.43	42.23	42.94	43.28	43.55	43.49	43.98	40.01	40.55
342	43.66	44.22	42.14	42.83	43.14	43.37	43.31	43.89	39.92	40.48
343	43.31	44.00	41.57	42.73	42.73	43.22	43.12	43.78	39.62	40.40
344	42.99	43.76	41.33	42.56	42.54	43.06	42.94	43.61	39.60	40.30
345	42.66	43.51	41.16	42.34	42.43	42.83	42.73	43.44	39.54	40.22
346	42.32	43.17	40.95	42.12	42.25	42.68	42.62	43.26	39.47	40.16
347	41.95	42.90	40.84	41.89	42.10	42.53	42.42	43.11	39.35	40.06
348	41.72	42.65	40.70	41.69	41.99	42.39	42.30	42.97	39.17	39.98
349	41.47	42.41	40.67	41.57	42.02	42.23	42.14	42.81	39.27	39.91
350	41.23	42.20	40.50	41.43	41.77	42.09	41.98	42.64	39.13	39.85
351	41.02	41.89	40.43	41.21	41.73	41.90	41.86	42.44	39.02	39.72
352	40.60	41.64	39.88	41.07	41.39	41.75	41.64	42.29	38.82	39.60
353	40.32	41.28	39.63	40.92	41.13	41.56	41.45	42.17	38.68	39.52
354	40.01	41.02	39.43	40.80	40.89	41.43	41.27	42.08	38.58	39.43
355	39.71	40.98	39.24	40.74	40.66	41.35	41.08	42.05	38.44	39.36
356	39.41	40.93	39.05	40.58	40.43	41.20	40.90	41.94	38.36	39.17
357	38.92	40.85	38.70	40.59	40.01	41.24	40.61	41.94	37.96	39.26
358	38.62	40.61	38.68	40.49	39.86	41.08	40.43	41.83	37.91	39.18
359	38.24	40.32	38.41	40.29	39.61	40.95	40.08	41.67	37.73	39.08
360	37.92	40.11	38.15	40.16	39.42	40.78	39.83	41.58	37.53	38.89
361	37.59	39.85	37.94	39.94	39.23	40.62	39.68	41.45	37.33	38.77
362	37.34	39.60	37.79	39.79	39.06	40.46	39.57	41.35	37.13	38.69
363	37.14	39.35	37.65	39.68	39.11	40.32	39.55	41.18	37.11	38.56
364	36.87	39.08	37.48	39.43	38.76	40.15	39.20	40.99	36.77	38.50
365	36.71	38.91	37.41	39.23	38.67	40.00	39.09	40.88	36.66	38.40
366	35.31	38.35	35.71	39.34	36.62	40.24	37.95	41.17	35.05	38.84

Figure 6

Key Points

Water levels in the Great Lakes have fluctuated since 1860. Over the last few decades, water levels have declined slightly for most of the Great Lakes (see Figure 1). The past few years, however, have shown notable increases toward the top of the historical range. At the end of 2023, water levels sat slightly above average for all of the Great Lakes.
Since 1995, average surface water temperatures have increased slightly for each of the Great Lakes (see Figure 2).
Recent increases in water temperature have mostly been driven by warming during the spring and summer months (see Figure 2). These trends could relate in part to an earlier thawing of winter ice (see the Lake Ice indicator).

Background

The Great Lakes, which are Lake Superior, Lake Michigan, Lake Huron, Lake Erie, and Lake Ontario, form the largest group of freshwater lakes on Earth. These lakes support a variety of ecosystems and play a vital role in the economy of the eight neighboring states and the Canadian province of Ontario, providing drinking water, shipping lanes, fisheries, recreational opportunities, and more.

Water level and water temperature are two important and interrelated indicators of weather and climate change in the Great Lakes. Water level (the height of the lake surface above sea level) is influenced by many factors, including precipitation, snowmelt runoff, drought, evaporation rates, and people withdrawing water for multiple uses. Water temperature is influenced by many factors, too, but most directly by air temperature.

In some recent years, high precipitation has contributed to higher-than-average and sometimes record-breaking water levels in the Great Lakes.¹ In other recent years, warmer surface water temperatures in the Great Lakes have contributed to lower water levels by increasing rates of evaporation and causing lake ice to form later than usual (see the Lake Ice indicator), which extends the season for evaporation.^2,3 Lower water levels in the Great Lakes forced ships to reduce their cargo tonnage by 5 to 8 percent between 1997 and 2000, which increased shipping costs.⁴ Lower water levels can also affect water supplies, the usability of infrastructure such as docks and piers, and shoreline ecosystems. Scientists who use computer models to simulate future climate change are not sure whether Great Lakes water levels will increase or decrease overall in the future, but they generally agree that there will be larger year-to-year variability, driven by periods of drought and extreme precipitation.¹

Another possible effect of warmer water, reduced ice cover, and increased evaporation is a corresponding increase in precipitation over nearby land, especially “lake effect” snow (see the Snowfall indicator).⁵ Rising water temperatures are also expected to expand the ranges of and give new advantages to some invasive species such as the zebra mussel, and to encourage the growth of certain waterborne bacteria that can make people ill.^6,7

About the Indicator

This indicator analyzes water levels and surface water temperatures in the Great Lakes. Water levels are recorded by gauges along the shore of each lake, some of which have been operated since the 1800s. Pre-1918 data came from one water level gauge per lake. Data since 1918 have come from a designated set of gauges in each lake. Figure 1 shows annual water level anomalies in each lake from 1860 to 2023; anomalies are differences, in feet, compared with a baseline (in this case, the 1981–2010 average). Lakes Michigan and Huron are combined because they are connected at the same water level.

Surface water temperatures are measured by satellites. Figure 2 shows annual average temperatures over the entire surface of each lake, along with the pattern of daily temperatures over the course of the year. This figure’s data begin in 1995, which was the first year with complete satellite data for all five lakes.

Indicator Notes

While climate change influences water levels, human activities such as dredging can also play a role. For example, the St. Clair River opening was enlarged in the 1910s, 1930s, and 1960s, contributing to greater outflows from Lakes Michigan and Huron.¹⁰ Similarly, natural year-to-year variability and other factors such as human use and wastewater discharges can influence water temperatures.

Data Sources

Water level data were provided by the Canadian Hydrographic Service and the National Oceanic and Atmospheric Administration’s Center for Operational Oceanographic Products and Services, and can be downloaded from: www.glerl.noaa.gov/data/wlevels/dashboard/. Surface water temperature data were provided by the National Oceanic and Atmospheric Administration’s Great Lakes Environmental Research Laboratory (satellite data at: https://apps.glerl.noaa.gov/erddap/info/glsea-avgtemps2/index.html).

Technical Documentation

Download related technical information (PDF)

References

Lamie, C., Bader, D., Graziano, K., Horton, R., John, K., O’Hern, N., & Spungin, S. (2024). Chapter 2: New York State’s Changing Climate. In New York State Climate Impacts Assessment (Interim version for public release).
Gronewold, A. D., Fortin, V., Lofgren, B., Clites, A., Stow, C. A., & Quinn, F. (2013). Coasts, water levels, and climate change: A Great Lakes perspective. Climatic Change, 120(4), 697–711. https://doi.org/10.1007/s10584-013-0840-2
Wilson, A. B., Baker, J. M., Ainsworth, E. A., Andresen, J., Austin, J. A., Dukes, J. S., Gibbons, E., Hoppe, B. O., LeDee, O. E., Noel, J., Roop, H. A., Smith, S. A., Todey, D. P., Wolf, R., & Wood, J. D. (2023). Chapter 24: Midwest. In USGCRP (U.S. Global Change Research Program), Fifth National Climate Assessment. https://doi.org/10.7930/NCA5.2023.CH24
Posey, J. (2012). Climate change impacts on transportation in the Midwest. In U.S. National Climate Assessment: Midwest Technical Input Report. Great Lakes Integrated Sciences and Assessments (GLISA). http://glisa.msu.edu/docs/NCA/MTIT_Transportation.pdf
Burnett, A. W., Kirby, M. E., Mullins, H. T., & Patterson, W. P. (2003). Increasing Great Lake–effect snowfall during the twentieth century: A regional response to global warming? Journal of Climate, 16(21), 3535–3542. https://doi.org/10.1175/1520-0442(2003)016%3C3535:IGLSDT%3E2.0.CO;2
Rahel, F. J., & Olden, J. D. (2008). Assessing the effects of climate change on aquatic invasive species. Conservation Biology, 22(3), 521–533. https://doi.org/10.1111/j.1523-1739.2008.00950.x
Kanoshina, I., Lips, U., & Leppänen, J.-M. (2003). The influence of weather conditions (temperature and wind) on cyanobacterial bloom development in the Gulf of Finland (Baltic Sea). Harmful Algae, 2(1), 29–41. https://doi.org/10.1016/S1568-9883(02)00085-9
NOAA (National Oceanic and Atmospheric Administration) Great Lakes Environmental Research Laboratory. (2024). Great Lakes water level dashboard. Retrieved March 14, 2024, from www.glerl.noaa.gov/data/wlevels/dashboard
NOAA (National Oceanic and Atmospheric Administration). (2024). NOAA CoastWatch Great Lakes node. Retrieved March 14, 2024, from https://apps.glerl.noaa.gov/erddap/index.html
Quinn, F. H. (1985). Temporal effects of St. Clair river dredging on lakes St. Clair and Erie water levels and connecting channel flow. Journal of Great Lakes Research, 11(3), 400–403. https://doi.org/10.1016/S0380-1330(85)71784-4

Text on this page is EPA’s own published wording (a U.S. Government work, not subject to domestic copyright), extracted from EPA’s published indicator page by the build-indicator skill. Data, chart code, and the full extraction pipeline are maintained in the great-lakes repository, which this page reads its data from directly.