Straddling the border of Nobleboro and Newcastle near the Maine coast, the Damariscotta Mills fish ladder is an unexpected local landmark—a centuries-old effort to protect the alewives that travel each spring from Great Salt Bay to the fresh water of Damariscotta Lake, where the fish spawn, that is still an economic engine for the small towns today. This story began with the alewife, an anadromous—or migrating from the sea to rivers to spawn—species of herring slightly larger than a human hand. The salty, bony fish was a dietary staple of…