In Slavic mythology, vodyanoy (Russian: водяно́й; IPA: [vədʲɪˈnoj], literally "watery"), vodyanoi, Belarusian vadzianik (Belarusian: вадзянік), Ukrainian vodianyk (Ukrainian: водяник), Polish wodnik, Czech and Slovak vodník, Bulgarian and Macedonian vodnik (Bulgarian: водник), Croatian vodanoj, Slovene povodni mož and Serbian vodenjak (Cyrillic: водењак), (Chuvash: Вутăш, Vutăş, Vudaş), is a male water spirit. Vodník (or in Germanized form hastrman) in Czech fairy tales is the same creature as the Wassermann or nix of German fairy tales. In many such languages the word is also used to mean the Aquarius zodiac sign.
Vodyanoy is said to appear as a naked old man with a frog-like face, greenish beard, and long hair, with his body covered in algae and muck, usually covered in black fish scales. He has webbed paws instead of hands, a fish's tail, and eyes that burn like red-hot coals. He usually rides along his river on a half-sunk log, making loud splashes. Consequently, he is often dubbed "grandfather" or "forefather" by the local people. Local drownings are said to be the work of the vodyanoy (or rusalkas).
When angered, the vodyanoy breaks dams, washes down water mills, and drowns people and animals. (Consequently, fishermen, millers, and also bee-keepers make sacrifices to appease him.) He would drag down people to his underwater dwelling to serve him as slaves.
In Czech, Slovene and Slovak folklore the features of the vodník are markedly different to the East-Slavic conception; he has a completely human constitution and habits, except for few differences – vodníci (plural of vodník) have gills, webbed membrane between their fingers and their skin is algae-green in colour (as well as their hair, which is typically of pale green tone). Their overall dress and appearance is weird, sometimes even resembling a vagrant; patchy shirts and (by modern standards) odd hats - often boaters with long speckled ribbons - are commonplace. They can withstand lingering for hours outside their ponds. When they do so, one can tell them unequivocally by their wet coat-tails from which water is dripping under all circumstances. The vodník's face is usually unshaven and it is not uncommon for a vodník to have a large, wet, tangled beard.