The approximate distance from the southern end of the St. Lawrence River to Duluth, Minnesota is about 1,000 miles (around 1,600 km) when measured along the general water route via the Great Lakes.

Understanding that distance

  • Educational geography resources that ask this exact question typically give an answer of “approximately 1,000 miles” as the standard.
  • These problems assume a ship or water-route style path from the lower/southern portion of the St. Lawrence, through the Great Lakes, up to Duluth on Lake Superior, rather than a straight-line “as the crow flies” distance.

Why it’s only approximate

  • The St. Lawrence system and Great Lakes have many possible measurement points, so the exact distance depends on:
    • The precise “southern end” location chosen on the St. Lawrence.
    • The exact harbor or dock position at Duluth.
  • Because of these variations, school and reference questions round the answer to a simple figure, about 1,000 miles , which is accurate enough for general geography and navigation discussions.

TL;DR:
If you see this question in a quiz or forum, the expected answer is “approximately 1,000 miles” from the southern end of the St. Lawrence River to Duluth, Minnesota.

Information gathered from public forums or data available on the internet and portrayed here.