I generally avoid swimming in freshwater, especially in the rural areas of the tropics... nevermind the pollution, it's also ridden with potentially dangerous bacteria and worms and god knows what else
Even the ocean is horribly polluted now. I saw sewage running freely into it numerous times in numerous countries, and even medical waste such as used syringes, needles, bandages washed out on the shore after the storm. It's so fucked up.