Fresh water clams are amazing creatures, unappreciated for their contributions to their local environment.  Once abundant in the many rivers and streams of North America, today they are not as easily found.  As prodigious filter feeders, they effectively kept the water clear and can be used to do the same in aquariums.  The trouble is, mollusks are unusually sensitive to chemical pollution, often dying after exposure to concentrations that won't harm fish.,(reply>), I live on the Oregon coast and near a river with a declining population of fresh water mussels, eel, and craw-fish in my lifetime. They are still here luckily. The ocean tide pools are not as fortunate . In my opinion it was declining as well and then the Fukushima accident  wiped out 90% of the tide pool life.