Russell Salsbury
former 50 Years a Software Engineer now in a hammock
Answered Feb 17, 2020
Duluth
, MN, is 2038 miles from the Atlantic Ocean. Another answer mentions
Tulsa
OK, but it is only 1162 miles. It might be a contender if you included the Gulf Intracostal Waterway, but I am not sure the Intracostal is deep enough for ocean going ships.
The obvious contender is the Amazon River which is navigable for large ships for at least 900 miles to
Manaus
and navigable to
Iquitos
, Peru, (2250 miles) for ships up to 18 feet draft weighing 3000 tons. I dont think that qualifies as a deep water port.
The
Nile
is blocked by the Aswan High Dam, so it doesnt make it. The
Murray River
is navigable for only about 1200 miles, way short.
The
Volga River
system is a interesting one to consider. The river plus some additional canals goes all the way from the
Baltic Sea
to the
Caspian Sea
, a distance of about 2300 miles, of via different canals to the
Black Sea.
20Geo addition: This site
might help you determine the correct answer