Oysters may seem like humble shellfish, but ecologically, they tower above many other species. They are a tasty food source for a variety of creatures, including humans. But more importantly, oysters help to filter pollutants from coastal estuaries, places where fresh river waters and ocean salt waters co-mingle. Fourteen out of 20 of the world’s largest cities are built near estuaries, and urban pollution, development and other factors are now threatening these delicate ecosystems. In response, some grassroots groups, are using oyster beds to help restore and stabilize damaged estuaries. New York and New Jersey Baykeeper is one of them.