Which river drains the Great Lakes and forms a significant waterway in eastern Canada?

The St. Lawrence River is the correct answer because it serves as a crucial outlet for the Great Lakes, draining their water into the Atlantic Ocean. This river is significant for both ecological and economic reasons. It connects the Great Lakes to the Gulf of St. Lawrence and facilitates navigation for ships traveling between the heart of North America and the ocean. The river supports a variety of ecosystems and serves as a vital waterway for commerce and transportation in eastern Canada and the northeastern United States.

Other rivers mentioned do not share this direct connection with the Great Lakes or serve as a principal waterway for that region. The Ohio River, for instance, flows into the Mississippi River system and does not interact with the Great Lakes. The Columbia River is located in the Pacific Northwest, far from the Great Lakes, and the Mississippi River primarily drains a different watershed in central North America, making it unrelated to the Great Lakes' drainage system.