The Kinneytown Dam in Seymour is shown Dec. 28. -STEVEN VALENTI/REPUBLICAN-AMERICAN SEYMOUR — It has been centuries since the Naugatuck River had runs of alewife, shad, striped bass or other fish that move from fresh water to the ocean and back again. A series of dams dating back to the 1700s helped fuel the Naugatuck Valley’s industrial might but prevented spawning runs of fish. The area’s industrial legacy also led to heavy pollution. Older locals recall the river running different colors depending on what the manufacturing mills were producing that day. With several dams removed and environmental regulations leading to cleaner waters, the scene is set for an environmental comeback, advocates say, and shad, striped bass, salmon, alewives and other fish are knocking at the door.