A decades-long effort to clean up the Chesapeake Bay, the nation's largest estuary, is showing signs of success. But scientists now say progress could be hindered by a hydroelectric dam, located on the Susquehanna River in northern Maryland.
The Conowingo Dam has been holding back pollution for nearly a century, but recent research shows it has filled up with sediment faster than expected.
"It's now at a point where it's essentially, effectively full," says Bill Ball, director of the Chesapeake Research Consortium. "The capacity's been reached."