Vermont Business Magazine The Vermont Department of Environmental Conservation (DEC) Wednesday announced a major environmental restoration project involving the use of an aluminum compound to control phosphorus pollution and decrease toxic cyanobacteria (blue-green algae) blooms on Lake Carmi. The project started the week of September 22, 2025.
“Lake Carmi’s alum treatment is the result of decades of collaborative watershed work,” said DEC Commissioner Misty Sinsigalli. “It marks a new chapter in Lake Carmi’s restoration, but ongoing community and state-level involvement will be essential to maintain water quality and protect this valuable natural resource.”
Lake Carmi is the fourth largest natural lake that is entirely within Vermont. In 2018, it was designated the state’s only Lake in Crisis due to the long-term presence of toxic algal blooms. These blooms are caused by excess phosphorus, which runs off into the lake from a range of sources (such as shoreland development, agriculture, streambank and road erosion, and wastewater).
Over the years, a broad coalition of partners has formed, including state agencies, local organizations, academia, the Town of Franklin, farmers, and residents. To date, the coalition has used many best management practices to reduce phosphorus runoff, such as:
- Agricultural runoff controls,
- Shoreland restoration projects,
- A zero-discharge wastewater system at Lake Carmi State Park, and
- Road improvements.
While these efforts have significantly reduced new phosphorus inputs, legacy phosphorus remains in lake sediments and fuels summer algal blooms. To address this, DEC and partners will apply aluminum sulfate, also known as alum, to the lake.
Alum removes phosphorus from the water by bonding with phosphates and settling on the lake bottom. This forms a barrier that stores phosphorus in lake sediments and prevents blooms.
Only two Vermont lakes (Ticklenaked Pond and Lake Morey) have had successful alum treatments in the past. These treatments are somewhat rare because they are costly and only work under specific conditions.
Alum treatments typically remain effective for many years. However, the long-term success of the treatment requires continued efforts to prevent new phosphorus inputs from entering into Lake Carmi. DEC and partners will continue this collaborative work and track the success of this treatment for years to come.
Learn more about the alum treatment at Lake Carmi online.
The Department of Environmental Conservation is responsible for protecting Vermont's natural resources and safeguarding human health for the benefit of this and future generations. Visit dec.vermont.gov and follow the Department of Environmental Conservation on Facebook and Instagram.
Vermont Agency of Natural Resources, Montpelier, Website.
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