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Massachusetts has 3,000 dams on approximately 8,000 miles of rivers.  Dams deplete and degrade fisheries, harm river ecosystems, and alter recreational opportunities on these rivers. 


How do dams damage rivers? First, 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. 


Second, 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. 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. 


Third, dams alter aquatic habitat. 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 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. 


Finally, 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.


Today, many dams that were once at the epicenter of a community’s livelihood are now old, unsafe or no longer serving their intended purposes. Many dams in Massachusetts  fall into this obsolete category. Most dams in Massachusetts were built in the 1700s and 1800s to power small mills. These dams have outlived their original purpose and are aging. Many dam owners are now choosing to remove their dams in order to reduce their liability and eliminate the long-term cost of inspections and repairs. The potential for ecological restoration benefits when these dams are removed is tremendous.  


In Massachusetts, we recognize that in an effort to decrease our dependence on fossil fuels, we must turn to further investments in renewable energy sources. It is equally imperative that we do not destroy the environment we are trying to save by rushing to develop low-emissions energy sources that will result in serious environmental harm, as well as high economic and societal costs. We can have – and must demand – energy that avoids carbon emissions, does not consume finite natural resources, and does not irreparably harm the environment.


How are we working on this issue at Mass Rivers?


We believe that the focus on hydropower dams in the coming years must not be on building new dams, but instead on maximizing efficiency, responsible operation, and environmental performance of existing dams. In Massachusetts, we have already tapped the significant majority of our hydropower potential. The few sites that remain would provide only marginal power benefits at great environmental cost. We must remember that rivers are part of our natural defense for addressing climate change. We need healthy rivers and the clean water and natural flood protection benefits they provide, in order to be resilient against the droughts, floods, and waterborne diseases that will increase with global warming. Likewise, fish and wildlife will need healthy, free-flowing rivers more than ever if they are to survive in a warming world. Building dams destroys the natural defense system that healthy rivers give our communities. 


If a hydropower dam can’t be operated economically while meeting modern, scientifically-based environmental standards, then either its operations should be improved, or the dam should be removed. New hydropower added to existing dams must be able to comply with all existing environmental laws and regulations; if it cannot, then it should not be developed. There are plenty of other sources of renewable energy that can be operated at a profit without harming the environment. 


At Mass Rivers, we are leaders in supporting both hydropower reform and investments in the removal of obsolete dams. We do this by championing policies that impose strict environmental conditions on hydropower facilities in Massachusetts and supporting funding for the state’s Division of Ecological Restoration, which is responsible for removing obsolete dams in areas that have the greatest potential ecological restoration benefit upon removal.