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How the Lakes Were Formed

3 | Great Lakes system profile: Elevations and depths

Graphic: Great Lakes system profile

Four of the five Great Lakes are at different elevations, leading like a series of steps toward the Atlantic Ocean. The five individual lakes are connected to each other through channelways, forming one system. Water continually flows from the headwaters of the Lake Superior basin through the remainder of the system.

The St. Marys River is a 60-mile waterway flowing from Lake Superior down to Lake Huron, descending more than 20 feet in elevation. Lakes Michigan and Huron are connected by the deep Straits of Mackinac and are considered to be one lake hydraulically with lake levels rising and falling together. The St. Clair and Detroit rivers, and Lake St. Clair between them, form an 89-mile-long channel connecting Lake Huron with Lake Erie. The fall between Lake Huron and Lake Erie is only about 8 feet. The 35-mile Niagara River links lakes Erie and Ontario, with the majority of the 325-foot difference in elevation occurring at Niagara Falls. The man-made Welland Canal also links the two lakes, providing a detour around Niagara Falls. From Lake Ontario, water flows into the St. Lawrence River, which converges with the Ottawa River near Montreal to flow to the Atlantic Ocean.

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