Massachusetts’ industrial past left behind fragmented rivers, tattered ecosystems and lifeless mill ponds. Putting the ecosystem back together again requires removing dams — lots of them.

Massachusetts is, for lack of a better description, constipated. Its 10,000 miles of rivers, streams and brooks are obstructed by nearly 3,000 dams, leaving the state susceptible to flooding, erosion and habitat degradation.

On average, there is one dam for every 3 miles of river, but the state’s antiquated impediments typically cluster in areas. With the exception of Nantucket, there are dams all across the state. The greatest numbers are in Worcester and Middlesex counties, while Berkshire, Bristol, Essex, Hampden and Norfolk counties each have 100 or more.

Southeastern Massachusetts, for example, is dotted with dams. The long-ignored, or unrealized, problem with river dams was highlighted during heavy rains in 2005, when the near-collapse of the Whittenton Dam, which holds back the Mill River, garnered national attention. If the 173-year-old wooden structure had breached, a 4-foot-high wall of water would have overwhelmed downtown Taunton.

Nearly 2,000 Taunton residents were evacuated, and schools and businesses were closed for several days.

The crisis — averted when the Army Corps of Engineers installed a temporary stone spillway to reinforce rotting wooden beams — led to the creation of Mill River Restoration, a broad partnership of environmental organizations and state and federal agencies. The partnership is designed to, among other things, restore the Mill River to a free-flowing river that provides passage for fish into Lake Sabbatia and the Canoe River watershed…

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