Lake St. Clair, situated between Michigan and Ontario, is often mistakenly identified as one of North America’s Great Lakes. Despite its substantial size and integral role in the regional ecosystem, it is not officially classified as a Great Lake. It serves as a vital hydrological link within the larger Great Lakes system, connecting two of the actual Great Lakes. This distinction arises from specific criteria used to define these immense freshwater bodies.
Defining the Great Lakes
The five Great Lakes—Superior, Michigan, Huron, Erie, and Ontario—are defined by their immense size, depth, and geological formation. They were primarily formed by the carving action of massive glaciers during the last ice age, approximately 14,000 years ago, which then filled with meltwater. They collectively represent the largest surface area of freshwater on Earth, encompassing over 94,000 square miles. The Great Lakes also hold nearly one-fifth of the world’s surface fresh water by volume.
Their considerable average depths, ranging from 62 feet for Lake Erie to 483 feet for Lake Superior, are a defining characteristic. These lakes exhibit sea-like characteristics, including significant depths, strong currents, and distant horizons. Lake Superior, for example, reaches a maximum depth of 1,300 feet, while Lake Ontario, the smallest by surface area, still has a maximum depth of 802 feet. The sheer scale and volume of these basins differentiate them from other large freshwater bodies in the region.
Lake St. Clair’s Connection to the Great Lakes System
Lake St. Clair is an integral part of the Great Lakes hydrological system, acting as a natural channel between Lake Huron and Lake Erie. The St. Clair River flows south from Lake Huron into Lake St. Clair, and the Detroit River then carries water from Lake St. Clair into Lake Erie. This continuous flow makes Lake St. Clair a crucial link in the Great Lakes Waterway. Approximately 97% of the water entering Lake St. Clair originates from the St. Clair River, highlighting its role as a conduit for the larger system.
The lake’s water residence time is relatively short, ranging from seven to ten days, a stark contrast to the much longer retention times of the Great Lakes, such as Lake Superior’s 197 years. This rapid water exchange means Lake St. Clair is more riverine in its characteristics than the deeper, more voluminous Great Lakes. Despite its functional importance, this rapid turnover and its dimensions prevent it from meeting the criteria for a “Great Lake” designation.
Unique Characteristics of Lake St. Clair
Lake St. Clair possesses distinct features that differentiate it from the Great Lakes. With a surface area of about 430 square miles, it is significantly smaller than even Lake Ontario, which is roughly 17 times larger by surface area. Lake St. Clair is also notably shallow, with an average depth of approximately 11 feet and a maximum natural depth of around 23 feet. For comparison, Lake Erie, the shallowest of the Great Lakes, has an average depth of 62 feet. This shallow depth contributes to warmer water temperatures.
The lake’s characteristics support a diverse ecosystem, making it a productive fishery and a significant habitat for migratory birds. Lake St. Clair is renowned for its sport fishing, contributing nearly one-third of the entire Great Lakes sport fishing catch annually. Additionally, the St. Clair River delta, located at the lake’s northern end, is one of the largest freshwater deltas in the world, providing important wetlands and wildlife habitats.