Anadromous fish such as alewives live in the ocean but must swim inland to fresh water to reproduce, a life cycle that was long part of North American aquatic ecology until water-powered mills and their dams blocked access to spawning grounds. Since the Hallville dam was built, fish coming up through Poquetanuck Cove could go no farther than the base of the dam; a first dam near this site was likely built in the mid-1700s, and after Joseph Hall, Sr. bought the property in 1857 and began an industrial woolen mill, the site was expanded by his sons Benjamin and Joseph, Jr., with the present dam probably first built around 1880 during a major enlargement project. The dam, the only barrier to fish between this point and the Atlantic Ocean, stood at a site where the mill employed 175 workers and produced 860,000 yards of cloth in 1888, was modified in 1920 for a new turbine and power system, remained in manufacturing use until the early 1960s, and saw the mill building on one side of the brook burn in 1978 and never be rebuilt. Because dams along migration routes devastated alewife populations, efforts in recent decades have reopened routes by removing some dams and building fish passage systems at others, and the Hallville fishway was constructed among the mill ruins as a steeppass design with sloped metal troughs and internal fins that create turbulence and reduce water force so fish can swim upstream to Hallville Pond, an approximately 11-acre spawning habitat. Completed in the spring of 2013, the fishway includes an underwater viewing window for recording fish passage, and the first alewife successfully ascended it at 1:21 a.m. on April 11, 2013.