Vodyanoy (or Water Spirit) Russian fairy tale character

Vodyanoy (or Water Spirit) is the King of the Deep.
In Slavic mythology, the Water Spirit is often an unattractive old man covered in silt and algae, and sometimes with a fishy tail. But he can change form.
He dwells in all kinds of reservoirs and wells, but you’ll most frequently find him in the pools near a water mill. In mythology, he’s considered evil, but in fairy tales, he is often not malevolent, though he sometimes tries to prevent the young hero from marrying his beloved, especially if she turns out to be the Water Spirit’s daughter. The Water Spirit appears in a tale “Tsarevitch Ivan and Princess Marfa.”