Lake Erie is one of the five Great Lakes, a massive, interconnected system of freshwater spanning the border between the United States and Canada. The lake is the shallowest of the five, with an average depth of about 62 feet and a surface elevation of approximately 570 feet above sea level. Lake Erie is not a terminus for its water, but rather a point in a continuous, downward-flowing hydrological chain that ultimately discharges into the sea.
Lake Erie’s Position in the Great Lakes Drainage Basin
Lake Erie forms a segment of the extensive Great Lakes drainage basin, receiving inflow from the upper lakes and local tributaries. Water naturally flows downhill through this system, moving from the highest lake, Superior, through Michigan and Huron, then into Lake Erie. Around 95% of Lake Erie’s water enters its western end through the Detroit River, which carries the combined discharge of Lake Huron and Lake St. Clair. This continuous influx dictates that the lake must have an outflow to maintain its level.
The Great Lakes basin acts as a chain of reservoirs, with water moving sequentially toward the ocean. Lake Erie sits at a lower elevation than Lakes Superior, Michigan, and Huron, making it a collection point before the water proceeds further east. The water has a relatively short retention time of about 2.6 years, the shortest among the Great Lakes. This rapid turnover rate means its entire volume is replaced quickly, underscoring that Lake Erie is an active conduit within the regional watershed.
The Water’s Path to the Atlantic Ocean
Water naturally exits Lake Erie at its eastern end, flowing into the Niagara River. The Niagara River travels north, transporting the lake’s massive volume of freshwater toward the next major receiving body. This course is interrupted by Niagara Falls, a natural barrier that creates a significant drop in elevation.
The water plunges over the falls, continuing its flow down the Niagara River gorge and eventually discharging into Lake Ontario. Lake Ontario is the last and lowest of the Great Lakes, sitting nearly 326 feet below Lake Erie’s surface elevation. The St. Lawrence River is the final natural outlet, serving as the primary drainage route for the entire Great Lakes system.
The St. Lawrence River flows northeast, passing through Quebec before widening into the Gulf of St. Lawrence. This gulf is a large estuary that merges with the Atlantic Ocean. Lake Erie’s freshwater naturally connects to the Atlantic Ocean through this sequence of rivers and lakes: the Niagara River, Lake Ontario, and the St. Lawrence River.
Connecting the Continents: The St. Lawrence Seaway
While the natural flow connects Lake Erie to the ocean, a man-made system exists for commercial navigation. The St. Lawrence Seaway is a complex system of channels, canals, and locks that allows large ocean-going vessels to travel deep into the North American interior. This massive engineering project was undertaken jointly by Canada and the United States, completed in 1959.
The seaway’s purpose is to bypass natural obstacles in the St. Lawrence River and the significant elevation drop between Lake Erie and Lake Ontario. The Welland Canal, a major component, circumvents Niagara Falls and its gorge. It uses a series of eight locks to raise or lower ships by the 326-foot difference in water levels. This navigational link allows ships to transit between the Atlantic Ocean and Lake Erie, and even further inland to the other Great Lakes.
The seaway transforms the Great Lakes system into a deep-draft marine highway, facilitating the movement of cargo like grain, iron ore, and steel products. This commercial connection is a separate but important answer to how the lake is linked to the ocean, providing a navigational path that complements the natural hydrological flow. The system enables vessels from overseas ports to reach the heart of the continent, connecting Lake Erie’s ports directly to global shipping routes.