These spirits are half-fish. They lurk in the mud at the bottom of freshwater lakes and also hide in the deep depths of wells, poisoning the water with their presence. The only way to prevent this is to sing to them.
We’re not sure what songs they like but you could try: "Would you like to swing on a star and carry moonbeams home in a jar — or would you rather be a fish?"
There is more but we feel this should be the responsibility of the Water Authorities.