Like most toponyms, as linguistic items, hydronyms are very conservative, with successor peoples often retaining the name given a body of water. For example, Mississippi has passed from Native Americans to contemporary Americans. Often a given body of water will have several entirely different names given to it by different peoples. For example, Vltava and Moldau are the Czech and German names, respectively, for the same river in central Europe.
Hydronyms from various languages can all share a common etymon. For example, The Danube, Don, Dniester, Dnieper and Donets rivers all contain the Scythian name for "river" (cf. don "river, water" in modern Ossetic).