Gold & Silver Forum - testing pond/lake water before eating fish

How can you test the water quality of ponds & lakes before eating the fish ? What kinds of tests should you do ? When I was a kid I never questioned the fish I pulled from various ponds, only if they were big enough to eat or not.

However, this one pond near my house is on land that has seen construction on some adjacent land. There is also a farm up the hill which I suspect will cause any "runoff" from the farm to end up in this pond. The pond has started to develop a bit of "scum" or moss that leads me to think its getting either fertilizer or animal waste runoff from the nearby farm. Its also near a road so who knows what trash has been thrown into it. The pond still has plenty of fros, turtles and smaller critters, so the water must still be livable for them. I remember a scene from "man vs wild" where Bear Grylls was looking for a safe place to get drinking water. He pointed out a small, flowing stream which had small crayfish so if they were present, the water was ok.

Im looking for some type of do-it-yourself kit that I can use to test a water sample. However, Im not even sure what to test for.

ideas ?