Lake Michigan–Huron

Lake Michigan–Huron
Lake Michigan–Huron lies in the center of the Great Lakes
Location	United States, Canada
Group	Great Lakes
Coordinates	45°48′50″N 84°45′14″W / 45.814°N 84.754°W / 45.814; -84.754Coordinates: 45°48′50″N 84°45′14″W / 45.814°N 84.754°W / 45.814; -84.754
Lake type	Glacial
Primary inflows	St. Marys River
Primary outflows	St. Clair River
Basin countries	United States, Canada
Surface area	45,300 sq mi (117,300 km2)
Max. depth	922 ft (281 m)
Water volume	2,029 cu mi (8,460 km3)
Residence time	100 years
Shore length1	3,250 mi (5,230 km) plus 2,215 mi (3,565 km) for islands
Surface elevation	577 ft (176 m)
Settlements	Milwaukee, Chicago, Cheboygan, Port Huron
1 Shore length is not a well-defined measure.

Lake Michigan–Huron (also Huron–Michigan) is the combined waters of Lake Michigan and Lake Huron, which are joined through the 5-mile (8.0 km) wide, 20-fathom (120 ft; 37 m) deep, open-water Straits of Mackinac. Huron and Michigan are hydrologically a single lake because the flow of water through the straits keeps their water levels in near-equilibrium. (Although the flow is generally eastward, the water moves in either direction depending on local conditions.) Combined, Lake Michigan–Huron is the largest fresh water lake by area in the world. If Lake Huron and Lake Michigan are considered two separate lakes, Lake Superior is larger than either.

The connection between Lake Michigan and Lake Huron through the Straits of Mackinac is 5 miles (8 km) wide and 120 feet (37 m) deep. This depth compares with the maximum depths of 750 feet (229 m) in Lake Huron and 923 feet (281 m) in Lake Michigan. Although the Straits create a pronounced bottleneck in the contours of the shoreline and a major constriction in the local bathymetry, defining two distinct basins, they are still deep and wide enough to allow the free exchange of water between the two sides. Because of the link through the Straits, Lakes Michigan and Huron have the same mean water level (in June 2015 it was 580 feet (177 m)).

The largest inflow to the system is the St. Mary's River from Lake Superior, and the main outflow is the St. Clair River to Lake Erie; both lie in the Lake Huron basin. The combined effects of seiches (resonant standing waves) and of differing weather conditions (atmospheric pressure, wind) over each basin act to drive water either way through the Straits on a variety of characteristic timescales, at amounts sometimes exceeding 75,000 m³/s (2,600,000 cu ft/s) for several hours in either direction. However, the long-term average flow through the Straits is eastwards at 1,500–2,000 m³/s (53,000–71,000 cu ft/s).