The St. Lawrence River is about 250 feet deep at its deepest point. In many sections, though, it is much shallower, especially in the upper river.

Quick Scoop

  • Deepest point: about 250 feet.
  • Where: near the American Narrows in the Thousand Islands region, north of Vanderbilt Island near Wellesley Island.
  • Other sections: the fluvial section is often only about 2 to 20 meters deep, while the estuary and gulf are much deeper.

If you want, I can also give you the depth by section, like Lake Ontario to Montreal, Quebec City, and the estuary.