Clams filter the water and check whether the water is polluted or clean
Maybe they could have alerted about  the lead contaminated water in Flint Michigan? A disaster that will affect the next generation. Lead Lowers IQ's in Children and increase crime rate in adults.<p>BTW, the invasive Zebra mussels have done a great job clearing up the Great Lakes. At times the water is so clear on a sunny day in the summer it can look tropical blue.