Diet for the big boys?

[Herpguy]

It's rather easy to know if you're catching food from "toxic water" or not. If there are no indicator species (mostly crustaceans) in a body of water you are collecting from, you need to be wary. Frogs and most animals cannot survive in a toxic environment, that's why frogs are a first-line indicator of pollution.

[Eridu Serpent]

I don´t think I´d chance it in most places, too many things used on the land which go into the water.

[Herpguy]

If you ever wanted to find out the quality for sure, a good test is to find an indicator species chart online. Go out with nets and capture as many invertebrates as you can, and then identify them later. Many insect larvae and crustaceans simply cannot survive if the pollution amount is more than negligible. If you find any low tolerance species, you are good to go.