I agree with pollutants, It's everywhere, from lead, copper, acids, oils, gas ..... anything you can think of. It's best to know where you're fishing at. Do some research, know where the water is coming from. How much houses around that area, are there industrial companies around, nuclear plants, farm piggeries,are sewers link to that Lakes or rivers, histories of that lake .... lots of contaminants ... you can take samples of the water If you like ... samples of soil, test the Ph level... lead ... and other metal contents to be more technical, etc.... before you decide to eat the fish ... or just Fish and chill out, C&R ! If you do all of the above ... you'll become a better fisherman tomorrow.