Vodyanik

Steve Prescott concept art.

Vodyanik is a water spirit in Slavik mythology described as resembling a creepy old man with a fat belly, a hat made out of reeds, and a skirt made out of rushes.

Vodyanik can be either a malevolent spirit or a benevolent spirit depending on which side of the bed he wakes up on. If the day starts nicely, he may just overturn fisherman's boats - but if the coffee machine isn't working, he's more likely to drown people trying to bathe in the shallows)