Dam Removal & Restoration
Our Approach
At OARS, we advocate for the removal of dams to promote healthier, free-flowing rivers and streams. These natural waterways are cleaner, cooler, and more ecologically connected. However, we understand that each dam is unique and requires a thorough, individualized assessment. Factors such as the dam’s role in the landscape, historical and scenic value, safety concerns, maintenance costs, and ownership must all be carefully considered. We aim to ensure that each decision reflects a balanced understanding of environmental benefits and community needs.
Benefits of Dam Removal
Builds Durable Climate Resiliency
- Reduces flooding upstream and mitigates flood hazards downstream
- Maintains streamflow during droughts, ensuring a stable water supply
Improves Water Quality
- Eliminates nutrient-rich sediments that contribute to the overgrowth of invasive plants
- Reduces excessive aquatic plant growth
- Provides cooler, flowing water with higher oxygen levels
- Eliminates stagnant water during droughts, preventing water quality degradation
Restores Wildlife Biodiversity
- Creates a healthier environment where native birds, mammals, and aquatic species can thrive
- Enhances habitats that support a diverse range of wildlife
Restores Habitat Continuity
- Allows aquatic life to spawn, find refuge during droughts, and migrate freely
- Supports recreational activities like fishing and boating and commercial fishing industries
Reduces Liability and Cost
- Eases the financial and maintenance burdens on dam owners and communities
- Access to funding and technical assistance for dam removal projects is widely available
Restoring Connectivity in the SuAsCo Watershed
OARS has developed a comprehensive Action Plan to prioritize dams for removal or fish passage installation, considering ecological and public safety factors. This ongoing initiative identifies the most beneficial connectivity projects from scientific and technical perspectives. Critical aspects of our approach include:
- Scientific and Technical Assessment: We use clear criteria and strategies to prioritize potential ecological restoration projects within the watershed
- Guiding Restoration Efforts: Our Action Plan serves as a roadmap for OARS and our partners as we collaborate with dam owners and local communities
- Ecological and Public Safety Benefits: By focusing on the most impactful projects, we aim to enhance habitat connectivity, improve water quality, and reduce flood risks
This targeted approach ensures that our efforts in the SuAsCo Watershed are effective and sustainable, maximizing the benefits for both the environment and the local communities.
SuAsCo Dams
Most dams in the SuAsCo watershed were built to power mills in the 1700s and 1800s and no longer serve that purpose. A few maintain reservoirs for water supply or state parks or are specialized flood-control structures; only two can generate electricity. The mill dams act like walls across the streams and rivers, turning them into a series of pond-like impoundments that warm and slow the flow of nutrient-rich water, fuel aquatic weed growth, and trap soft sediments behind each dam as much as 10 feet deep.
Aquatic weeds, particularly filamentous green algae, milfoil, and water chestnut, are not just a nuisance. They block sunlight and decrease the oxygen in the water necessary for aquatic life. They out-compete native aquatic vegetation and can make river recreation impossible in the summer. As the plants die back and sink to the bottom in the fall, the nutrients they incorporated settle into the sediments, ready to fuel another year’s growth. This recycled phosphorus is a significant source of water pollution.
Dams also block the movement of fish and other river wildlife that need to be able to move up and down streams to find food, refuge from drought and heat, and places to breed. These rivers were once home to multitudes of migratory fish that swim from the ocean into fresh water to breed or mature. OARS is working to restore these species that are important to the Gulf of Maine fisheries, recreational fishing, and local river ecology: river herring (blueback herring and alewife), American shad, American eel, and sea lamprey.
Concord Watershed Dams
Assabet Watershed Dams
Dam Removal & Restoration Projects in Our Watershed
Sudbury Watershed Dams
Massachusetts Dams
Massachusetts is home to over 3,000 dams, but only 37% of them received a satisfactory or fair rating in their most recent inspections, according to federal data. A significant portion, 20% (or 267 dams), were rated as poor, indicating the need for remedial action, while 3% (35 dams) were deemed unsatisfactory, requiring immediate or emergency measures. Of these, seven are classified as high hazard, posing a risk to human life if they fail. In the past 15 years, around 70 dams have been removed across the state. Notably, only a small percentage of these dams serve purposes such as providing drinking water, flood control, or recreational opportunities; the majority of dams in Massachusetts no longer fulfill any functional role.
National Dams
In 2024, the removal of 108 outdated and unsafe dams across 27 states reconnected over 2,528 miles of rivers, improving habitats for fish and wildlife. Among these projects was the historic restoration of the Klamath River, led by local communities and tribal nations. Dam removal enhances river health, public safety, and local economies, creating jobs and significant economic benefits. Since 1912, 2,119 dams have been removed in the US, with Pennsylvania (27 dams), Michigan (10 dams), Minnesota (7 dams), and Virgina (7 dams) leading in 2024 (Massachusetts was 3rd in 2023 with six dams removed).