Thousands of small, often obsolete dams are blocking fish migrations across the United States. In this piece, Ben Goldfarb explores the growing movement to remove these barriers—despite political, economic, and emotional obstacles. He asks, “Can government agencies and conservation groups pick up the pace of dam removal while fish are still around to benefit?”

The Eastern Seaboard’s most enthusiastic purger of dams has long been Plymouth, Massachusetts, and one weekend I visited during its Herring Festival, a celebration of the resurgent alewife population that annually runs up Town Brook, the stream at Plymouth’s heart. The day was cool and damp, and I followed a posse of dads in Red Sox sweatshirts and kids in rainboots up the path that paralleled the creek. Someone had chalked “LOOK FISH” on the asphalt, and I glanced streamward to find alewives holding in small pods, weaving around each other in their effortless way.