The story
European spelling of an Algonquian name, variously claimed to mean "river of swans", "place where people trade" or "place to which tribute is brought". The natives called the river above the falls Cohongorooton, "river of geese", and that area was renowned in early years for an abundance of both geese and swans. The spelling of the name has been simplified over the years from Patawomeke to Patowmack in the 18th century and now Potomac. The river's name was determined officially as Potomac by the US government's Board on Geographic Names during 1931.
Etymology from Wiktionary, CC BY-SA 4.0.