A fall line is a region where neighbouring rivers all have waterfalls or rapids in the same places down their valleys.

A fall line separates the coastal plain of eastern America from the hill lands of the Appalachians.

Waterfalls and rapids on the fall line make navigation of the rivers difficult. Many east coast cities were founded around rivers on this fall line because it was the head of river navigation from the sea.

There are also fall lines in Sweden and in the English Pennines.