I read about the Cuyahoga river, more specifically this fragment:

Animal life does not exist. Only the algae Oscillatoria grows along the piers above the water line.

So I was wondering which organism would be best at surviving extremely polluted environments? Is there such a thing as a completely dead river, or will there always be some extremely resilient organism that doesn't care (or maybe even thrive). I know about tardigrades, but as I understood they are only this resilient when going into cryptobiosis. I'd be interested in organisms that don't "cheat" but rather have the time of their life in the dirtiest of rivers (or any other hostile environment for that matter).