People who read way too much on the internet (like me) learn to look for red flags and dismiss any "facts" that seem sketchy. That's a good thing. Then there's Tom Scott (previously at Neatorama), who makes a living by going there and finding out for himself whether something that sounds strange is true or not. So he went to Warsaw to find out if the city uses clams to monitor water quality. It's true! And the process they use is quite interesting. If the water is good, they will open their shells to bathe in it. If something is wrong, they will close up to protect themselves. It's like an early warning system that will alert human experts if the water needs more thorough testing.
The people who run the waterworks also refer to the clams as their colleagues. Instead of eating them after their stint has ended, they release them into the wild. I bet those folks never eat clams.