The Great Lakes represent a singular freshwater system, holding one-fifth of the world's surface freshwater supply. Understanding what lakes make up the great lakes is essential to grasp the scale and importance of this transboundary resource shared by the United States and Canada.
The Five Primary Lakes
The core identity of the system is defined by five massive bodies of water, each with its own distinct characteristics and ecosystems. These are the fundamental components that form the foundation of the Great Lakes Basin.
Superior, Michigan, and Huron
Lake Superior stands as the largest by surface area and the deepest, holding the greatest volume of freshwater. Lake Michigan is the only one located entirely within the United States, while Lake Huron connects to Superior via the St. Marys River and features the expansive Georgian Bay.
Erie and Ontario
Lake Erie is the shallowest and most biologically productive, warming quickly in summer and supporting major fisheries. Lake Ontario lies downstream of Erie, acting the final reservoir before water exits the system through the St. Lawrence River toward the Atlantic Ocean.
Connecting Channels and Drainage The lakes are not isolated; they are linked by a series of rivers and channels that dictate the flow of water and navigation. This hydrological connection creates a single, dynamic system where the outflow of one becomes the inflow of the next. Upstream Lake Downstream Lake Connecting Waterway Superior Michigan/Huron St. Marys River Michigan/Huron Erie St. Clair River, Lake St. Clair, Detroit River Erie Ontario Niagara River Ontario St. Lawrence River St. Lawrence River The Broader Basin
The lakes are not isolated; they are linked by a series of rivers and channels that dictate the flow of water and navigation. This hydrological connection creates a single, dynamic system where the outflow of one becomes the inflow of the next.
Upstream Lake | Downstream Lake | Connecting Waterway
Superior | Michigan/Huron | St. Marys River
Michigan/Huron | Erie | St. Clair River, Lake St. Clair, Detroit River
Erie | Ontario | Niagara River
Ontario | St. Lawrence River | St. Lawrence River
While the five main lakes are the most prominent features, the total system includes additional waters that drain into the mix. These smaller lakes and tributaries contribute to the overall watershed, influencing water quality and habitat diversity across the region.
Shared Resources and Management
The lakes form the economic and environmental backbone of the region, supporting industry, agriculture, and millions of residents. International agreements and binational programs are critical for managing this shared asset, ensuring that the water remains safe and sustainable for future generations who depend on it.
