The River Gambia is one of the most navigable of all African rivers.
Spain has only 7 navigable rivers, none of which is near the capital, Madrid.
In 1972, the American Congress passed the Clean Water Act, forbidding discharges of pollutants into navigable waters.
The river is navigable for the first few miles, but after that it is impossible to pass through in a boat because of the rocks and the rapids.