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Dam Removal Brings Life Back to River

Until recently, Maxwell Pond on the Black Brook in Manchester, New Hampshire was considered “impaired.” The state added it to the U.S. Environmental Protection Agency’s (EPA’s) national list of impaired waters in 2002 because the pond could not support aquatic life.

How did the pond reach this unhealthy state? The pond itself was created in the early 1900s, when a dam was built across Black Brook to create an area for ice harvesting. The pond was originally more than five acres in size, with a depth of about 12 feet. But poor stormwater controls led to excess sediment runoff into the pond.

By 2002, sediment had filled the pond: it was only three feet deep, and the water behind the dam was warm and stagnant. The amount of dissolved oxygen in the water was so low it couldn’t support aquatic life – hence its addition to the “impaired waters” list. We decided to take action: with funding from NOAA, EPA, and the state, project partners (including American Rivers and Trout Unlimited) removed the dam in February 2009.

With the dam’s removal, the pond disappeared – all the water that had been trapped behind the dam to create the pond flowed downstream. Water was able to flow downstream from Manchester to the Merrimack River for the first time in more than 100 years.

With the river flowing freely, the water temperatures dropped and oxygen levels returned to normal. In 2010, New Hampshire removed Maxwell Pond from the list of impaired waters. The river can support fish and wildlife once again.

Deep-Sea Coral

Heavy equipment breaches the Maxwell Pond dam on Black Brook in New Hampshire.

Credit: Steve Landry, New Hampshire Department of Environmental Services.