The rooftop swimming pool stinks.

Is there mud down there? It may be fish excrement and other sundries accumulated at the bottom of the pond for a long time, and gas (biogas, hydrogen sulfide, etc.) is produced by fermentation. Because of the weather (air pressure, etc. ), the dissolved oxygen in the water is low and these sundries are toxic, so the fish must die to pieces. Blister and turbidity are obvious manifestations. Before the fish dies, there should be a floating head phenomenon, and there may be black material fragments floating on the water.