How big is Lake Saint Clair?

Lake Saint Clair is a moderately sized freshwater lake located in the Great Lakes region of North America, nestled between the U.S. state of Michigan and the Canadian province of Ontario. While it is not one of the five official Great Lakes, its size and strategic location make it a significant part of the Great Lakes Waterway, serving as a crucial connection between Lake Huron (to the north) and Lake Erie (to the south). When it comes to its physical dimensions, Lake Saint Clair is notable not for its depth but for its broad, shallow expanse and navigational importance.

Surface Area

Lake Saint Clair spans a surface area of approximately 430 square miles (1,114 square kilometers). It is roughly 26 miles (42 kilometers) from north to south and about 24 miles (39 kilometers) from east to west. These dimensions give the lake a roughly circular or oval shape, often described as pancake-flat due to its shallow depth and wide footprint.

To put its size into perspective:

⦿ It is larger than Lake Tahoe (191 square miles) and Lake Pontchartrain in Louisiana (630 square miles), but

⦿ It is much smaller than the five Great Lakes, the smallest of which—Lake Ontario—covers around 7,340 square miles.

Depth

One of the most defining characteristics of Lake Saint Clair is its shallow depth:

• Average depth: About 11 feet (3.4 meters)
• Maximum natural depth: Around 21 feet (6.4 meters)
• Dredged channel depth: Up to 27 feet (8.2 meters)

Because of its shallowness, the lake can warm up quickly in summer and freeze over easily in winter. The shallow nature also historically made navigation difficult, necessitating the construction of a 27-mile-long shipping channel maintained by the U.S. Army Corps of Engineers to accommodate freighters and commercial vessels traveling between the upper and lower Great Lakes.

Volume

Due to its shallow depth, Lake Saint Clair holds a relatively modest volume of water. Its total water volume is estimated to be around 1.85 cubic miles (7.7 cubic kilometers), which is a fraction of the volume of any of the five Great Lakes.

Shoreline and Watershed

The shoreline of Lake Saint Clair stretches for approximately 160 miles (260 kilometers), including its U.S. and Canadian sides. The lake is part of a much larger Lake Saint Clair watershed, which covers over 7,000 square miles and includes several tributary rivers—most notably the Clinton River in Michigan.

Comparison to Other Lakes

Lake	Surface Area (sq mi)	Average Depth (ft)	Max Depth (ft)
Lake Saint Clair	430	11	21
Lake Ontario	7,340	283	802
Lake Erie	9,910	62	210
Lake Tahoe	191	1,000	1,645

As this table illustrates, Lake Saint Clair is significantly shallower and smaller than the Great Lakes but remains an integral link in the Great Lakes system due to its location.

Conclusion

Lake Saint Clair is not a giant in size compared to the Great Lakes, but its 430 square mile surface area and central position make it a vital component of the region’s hydrology, ecology, recreation, and commerce. Its shallow, expansive form has led to extensive management efforts to maintain navigability, while its broad shoreline supports vibrant communities and ecosystems on both sides of the U.S.-Canada border.