Coming down

The history of dams on the Jones River begins in the 1640s, with the first granting of a “privilege’’ to harness water power with a dam. One proviso was the removal each spring of the log structures to allow passage for spawning fish.

But with the Industrial Revolution and the advent of concrete, the rewards of full-time productivity from permanent dams overrode the centuries-old understanding of the importance of a self-replenishing fish population. In the early 1900s, dams at Elm Street, Wapping Road, and Forge Pond were made permanent with poured concrete.

Over the years, there have been attempts to maintain the aquatic population by annual restocking - without success. The last herring count, taken by watershed association volunteers during the latest spawning season at the Elm Street fish ladder, found 363 from April 6 to May 29, translating to 3,011 herring in the entire river, based on state projections, said Alex Mansfield, the association’s ecology program director.

“We should be seeing hundreds of thousands and shouldn’t even be able to count the fish when they’re running,’’ said duBois.

The dams have also harmed the water’s health, with blocked water warming in the sun to the detriment of native fish, while proving a boon to bacteria and invasive plant species. The depleted oxygen levels and warm water temperatures make it unsuitable spawning grounds for those fish that do manage to reach it.

The dams also trap sediment that can contain contaminants from decades of dumping by the mills, such as the Mayflower Worsted Co., which closed at Wapping Road in the 1960s. Pollutants from outside sources, such as fertilizer and road run-off can also settle in the stilled water.