Hello Kitty no Fushigi na Mizuumi

Overview

Kitty and Mimmy hear about the mysteries of a lake when they go up to fish with their Papa. At night they discover a Loch Ness monster like creature and fairy. The monster does not want to live in the lake anime due to illegal dumping which is also causing the fish to leave. The girls recruit a grandmother witch to help the monster gain the ability of flight so it can leave. But it asks the witch to also clear the lake of debris too. Now it can live happily in its lake.

Source: AniList