What is the approximate distance from the southern end of the the St. Lawrence River to Duluth, Minnesota

The distance from St. Lawrence River to Duluth is approximately 800 miles.

Explanation:

St. Lawrence is a large river in the mid regions of North America and flows in a north east direction. The river connects the Great Lakes to the Atlantic Ocean and also forms the drainage outflow of the Great Lake Basin. Duluth is a city in Minnesota and is essentially a port city. The river flows through the coasts of Duluth and becomes tidal.