top of page


Dam on Ipswich River in 2015 by Bill Parker

Massachusetts has 3,000 dams on 8,000 miles of rivers.

300 of those dams are considered high hazard. 

Dams deplete and degrade fisheries, harm river ecosystems, and alter recreational opportunities on these rivers.

To power Massachusetts' economy in the 1700s and 1800s, dams were built around the state to power mills. Those mills powered us through the industrial revolution and were the center of their communities. Today, most of those dams are obsolete: unsafe and no longer serve their intended purpose. In fact, many of these old dams are at risk of failing which could cause significant economic losses or death. Learn more about dams that could be at risk of failure near you>>

How do dams damage rivers?

Dams prevent fish migration

This limits their ability to access spawning habitat, seek out food resources, and escape predation. Fish passage structures can enable a percentage of fish to pass around a dam, but their effectiveness decreases depending on the species of fish and the number of dams fish have to traverse. 

fish graphic

Dams alter river flows

Aquatic organisms, including fish such as trout and river herring, depend on steady flows to guide them. Stagnant reservoir pools that are created by dams disorient migrating fish and can significantly increase the duration of their migration. Dams can also alter the timing of flows.

river waves graphic

Some hydropower dams, for example, withhold and then release water to generate power for peak demand periods. These irregular releases destroy natural seasonal flow variations that trigger natural growth and reproduction cycles in many species. 

Dams fundamentally change the way rivers function. They can trap sediment, burying rock riverbeds where fish would typically spawn. Gravel, logs, and other important food and habitat features can also become trapped behind dams. This negatively affects the creation and maintenance of more complex habitat (e.g., riffles, pools) downstream.

Dams alter aquatic habitat

seaweed graphic

Dams that divert water for power and other uses also remove water needed for healthy in-stream ecosystems. Peaking power operations can cause dramatic changes in reservoir water levels. This can leave stretches below dams completely de-watered. 

Dams significantly alter water quality and temperature

Slow-moving or still reservoirs can heat up, resulting in abnormal temperature fluctuations which can affect sensitive species. This can lead to algal blooms and decreased oxygen levels. Other dams decrease temperatures by releasing cooled, oxygen-deprived water from the reservoir bottom.

temperature gauge graphic

Dam Removals

Removing an old dam can reverse many of the negative impacts on fish and wildlife. For the dam owner, removing the structure reduces their legal liability and saves them dam maintenance costs. If your property has an obsolete dam, consider the benefits of removing it >>

In Massachusetts, we're lucky to have the Division of Ecological Restoration, a small but dedicated team that analyzes benefits of ecological restoration, removes dams, and works with municipalities on climate resilience projects. Check out their project map, including dam removals across the state >>

DER has rated every dam in the state for the ecological restoration benefits that removing the dam would provide. See if there's one near you >>

The photo at right is of the Elm Street Dam Removal on the Jones River in Kingston, MA. In October 2019, the river flowed freely through the site for the first time in over 300 years, opening up 24 river miles to native fish as they swim upstream from the ocean. This victory came after years of hard work by local advocates like the Jones River Watershed Association.

Elm Street Dam Removal project in Kingston MA in 2019

Hydropower & the Fossil Fuel Transition

The Turner's Falls dam in Greenfield, MA operated by FirstLight Power.

The Turner's Falls dam in Greenfield, operated by FirstLight Power. 

We can have - and must demand - energy that avoids carbon emissions, does not consume finite natural resources, and does not irreparably harm the environment.

As we continue our battle with climate change, the focus should not be on building new dams, but instead maximizing efficiency of our existing hydropower, responsible operation, and environmental performance of dams.

In Massachusetts, we've already tapped the significant majority of our hydropower potential. The few remaining sites would provide only marginal power benefits at great environmental cost. Rivers are part of our natural defense for addressing climate change: they provide flood protection and resilience against droughts. Likewise, fish and wildlife will need healthy rivers more than ever to survive a warming world.


The hydropower industry must be responsible. If a hydropower dam can’t be operated economically while meeting modern, science-based environmental standards, then either its operations should be improved, or the dam should be removed. New hydropower added to existing dams must comply with all existing environmental laws and regulations; if it cannot, then it should not be developed. 

How are we working on this issue at Mass Rivers?

At Mass Rivers, we support both hydropower reform and removing obsolete dams. We champion policies that impose strict environmental conditions on hydropower facilities in Massachusetts and support funding for the state’s Division of Ecological Restoration, which removes old dams to restore natural ecosystems.

bottom of page