around here, it was similar with the lakes.
DDT, farm run off, chemical contamination changed that.
There are some nasty spots South East of the Twin Cities where the various types of pollution converge. And a couple communities directly in the cross section. The Mississippi pollution with the fish was mercury from talking to old timers, fish absorb it easy. The petroleum refiner by product drifts east over same communities. More recently, 3M forever chemicals found in the soil and watersheds of the same communities.