Worried about ducks

Hi everyone,

My neighbour acquired a duck around Christmas time and today 2 more have appeared.  We live in terraced houses with very small back yards and they only have a tiny plastic paddling pool - about 1 meter in diameter and the water is about 10 cm deep and always filthy.

I was concerned when they were only keeping 1 duck in that environment but now there are 3 I am really worried its not healthy for them.

Does anyone have any advice?

Many thanks in advance.