Which river does Lake Ontario drain into?

Lake Ontario drains into the St. Lawrence River, making it the correct answer. This river is a crucial waterway that flows northeast from Lake Ontario, facilitating the movement of water from the Great Lakes system into the Atlantic Ocean. The St. Lawrence River serves as a primary outlet for Lake Ontario, connecting it with the other Great Lakes and beyond.

Understanding the role of the St. Lawrence River is vital in the context of hydrology and geographies surrounding the Great Lakes. It not only plays a vital role in local ecosystems but also supports major shipping routes and contributes to both the economy and the environment of the region.

The other rivers listed are not linked as drainage points for Lake Ontario. For instance, the Ohio and Mississippi rivers are part of the larger Mississippi River system and are not connected to the Great Lakes directly. The Niagara River, while it flows from Lake Erie to Lake Ontario and is significant due to the iconic Niagara Falls, does not serve as an outlet for Lake Ontario but rather as an input to it from the other Great Lake.