Built to generate power for industry in the 18th and 19th centuries, dams served an important role in the history of the Charles River watershed. However, dams slowed the flow of the Charles River, hampering its ability to cleanse itself. Dams also prevented migratory river herring from reaching upstream reaches of the river to spawn. While some Charles River dams provide flood control, many of the dams on the Charles River bring more problems than benefits. When dams become obsolete, their removal can benefit rivers and the surrounding communities. These Frequently Asked Questions discuss the benefits and challenges of dam removal.
Dam Removal FAQ
As river herring attempt to traverse the fish ladder at Watertown Dam, they make easy prey for gulls.
- How many dams are on the Charles River?
- There are currently 109 dams in the Charles River watershed, 23 of which are on the Charles River. 13 of the dams on the Charles are owned by the state, 3 are owned by local towns and cities, 1 is owned by the U.S. Army Corps of Engineers, and 6 are privately owned.
- Why were these dams built?
Most of these dams were built in the 1700's and 1800's to generate power for mills and factories along the Charles River. For example, the Moody Street Dam in Waltham was originally built to power a paper mill and was then adapted for a larger cotton mill.The Charles River Dam at the mouth of the river and the older dam it replaced were built to keep the tide from entering the Charles River and to prevent flooding. These dams converted the lower Charles River from an estuary into the man-made Charles River basin.
What purpose do dams on the Charles River serve now?
- At best, 12 of the dams currently help control flooding, and none generate power. The Charles River Dam provides flood control and shapes the lower Charles River basin as we know it today. The Moody Street Dam in Waltham allows for some control of streamflow. Many of the dams no longer serve a purpose.
What effect do dams have on fish and wildlife?
- Dams prevent river herring, including the American shad, from migrating upstream to lay their eggs. Fish ladders installed at some dams help fish swim upstream, but each dam makes the trip more difficult, and some fish never make it to their spawning grounds. Dams also alter water clarity and chemistry, upon which the reproductive cues and behaviors of many fish species are based. Dams contributed to the decline of migratory fish populations in the Charles River and are hindering there populations them from becoming re-established, especially the American shad. Dams create stagnant water, which is susceptible to temperature increases and loss of oxygen, harming wildlife.
Removal of the Old Mill Dam on Pearl Street in Bellingham began this week.
- What are some of the benefits of dam removal?
- Removing a dam restores the free flow of water and sediment. It also allows fish and other wildlife to travel between portions of the river and can help migratory fish populations rebound. Removing a dam eliminates expensive maintenance costs and removes the risk of people being injured around a deteriorating dam. The Massachusetts Department of Conservation and Recreation’s Office of Dam Safety has rated three of the dams on the Charles as having high hazard potential, eleven of the dams as having significant hazard potential, and five of the dams as having low hazard potential. Dams that have high or significant hazard potential and no longer serve a purpose make good candidates for removal.
- How will dam removal change the surrounding area?
- Removing a dam will generally cause the river to narrow and deepen in that area, eliminating or reducing the "mill pond" behind the dam. Dam removal may reduce flooding.
- What are some of the challenges that keep dams from being removed?
- Dam removal can be costly and time-consuming for the owner of a dam. However, funding and technical support from State and Federal agencies can help make dam removal feasible. In some cases, members of a community may oppose dam removal out of a desire to preserve local history. A well-designed dam removal project can preserve aspects of the history while removing the dam in order to improve safety and river health.
- Are there plans to remove any dams on the Charles River or have any already been removed?
- Yes, the Old Mill Dam in Bellingham was removed in 2017. Removal of the Watertown Dam was recently added to the list of designated Priority Projects of the Division of Ecological Restoration at CRWA's recommendation.