The primary outlet for the Great Lakes is the Saint Lawrence River.

The Saint Lawrence River is a system of locks and canals that connects the Great Lakes to the Atlantic Ocean via the St. Lawrence River. This waterway allows ships to travel between the Great Lakes and the broader international shipping network. The Seaway plays a critical role in the transportation of goods such as iron ore, coal, and grain, contributing to the economies of both the United States and Canada. The flow of water from Lake Ontario into the St. Lawrence River serves as the natural outlet for the entire Great Lakes system.