Androscoggin Lake Bloom FAQ’s

August 29, 2024

FAQs about the Androscoggin Lake Algal Bloom: 


Are we going to see this every year?

We do not yet know. Though Androscoggin Lake has experienced lake-wide algal blooms four out of the last five years, it is still considered a fairly infrequent bloomer, with six documented lake-wide algal blooms in the nearly 50-year historical monitoring record. Since 2022, we have been studying the lake much more thoroughly to better understand what is causing the bloom. Additional information about what we are doing can be found in below.

What makes the water green?

Cyanobacteria, originally called blue-green algae, because dense blooms of it will turn the water green or blue-green in color. Cyanobacteria are a natural and important part of the lake ecosystem, and can be found in all lakes all over the world. However, when nutrient concentrations, particularly phosphorus, are high enough and conditions are just right, their population can explode. The result is what we call a “cyanobacteria bloom” or “algal bloom.” Maine DEP defines a “nuisance algal bloom” when water clarity is less than 2 meters, and a ”harmful algal bloom” when water clarity is less than 1 meter.

Is it dangerous to swim in it?

The DEP recommends not swimming if you are standing in water chest deep (4-5 feet) and you can’t see your toes because the water is so green. Or, if you are looking into water that is 4-5 feet deep and can’t see the bottom of the lake because the water is so green, you should not go in. Any area where algae has accumulated, forming a scum, should be avoided by humans (especially young children), pets, and livestock.

Is the water toxic?

It may be. Though some species of cyanobacteria can produce toxins under certain conditions, not all cyanobacteria blooms are toxic. While heavy growths or scums often show detectable levels of toxins, only the most intense blooms create a potential for significant toxin exposure for humans and animals. The most common and best studied toxins are microcystins. 

Maine DEP has monitored cyanotoxins in lakes across the state since 2008. Of all the samples they have collected thus far, only a few open-water samples have exceeded EPA’s Drinking Water Standard for the algal toxin microcystin for infants and non-school-age children, but not the standard for school-age children or adults. No open-water samples have exceeded the Recreational Standard – even when taken from lakes with algal blooms that are chronic and severe. The same was true in Androscoggin Lake.

However, Maine DEP has detected very high concentrations of microcystin in algal scums that accumulate along the shore in other Maine lakes. For this reason, these areas should be avoided by humans (especially young children), pets, and livestock.

Through Maine DEP samples collected in September, 2025, the lake was found to have microcystin in water samples collected along the shore and from scum.  Microcystin levels exceed safe limits for drinking water and recreation.

Does it affect wildlife?

In the case of a severe bloom that is producing toxins, fish and other wildlife, such as loons, could be negatively affected by high levels of toxins. This could result from consuming the water and or algae directly, or having consumed other organisms that have consumed the water or algae. Additionally, loons are visual predators. If they are not affected by toxicity, their hunting could be disrupted by the reduction in water clarity.

Algal blooms in general can exacerbate problems with low oxygen levels in lakes, which can be detrimental to fish and other aquatic organisms that require an adequate supply of oxygen to survive. As algae die and sink to the lake bottom, the decomposition process will use up the oxygen in the deep waters of the lake. More algae in the water means more decomposition and a greater amount of oxygen depleted from the water.

What causes the algae to bloom?

Phosphorus is the culprit, and is the nutrient that most influences the growth of algae in lakes. Its natural occurrence in lake water is very small, and even the smallest increases in phosphorus in lake water can cause substantial increases in algal growth. Sources of phosphorus include human and animal waste, agricultural and residential fertilizers, and soil from erosion in the surrounding watershed. All of these sources can deliver phosphorus to the lake via stormwater runoff either directly from shorefront property, or indirectly through ditches, culverts, or streams that drain to the lake.

Another major source of phosphorus is the sediments at the lake bottom. In the summer months, low oxygen levels in the deep waters of the lake can cause a chemical reaction to occur at the sediment surface. This reaction causes the sediment to release phosphorus into the water column — a phenomenon known as “internal phosphorus loading”. To learn more, please read our reports on Androscoggin Lake’s water quality here: https://30mileriver.org/androscoggin-lake/

Does this relate to the milfoil problem?

No, the algae, or cyanobacteria, causing the algal bloom are very small, planktonic plants that are free-floating in the water. The invasive variable leaf milfoil found in the inner cove of Androscoggin Lake is an aquatic plant rooted in the sediments. While cyanobacteria and the milfoil both favor warm, nutrient-rich water, one does not cause the other. However, the algal blooms in recent years have created a challenge for late-season management of the milfoil infestation and removal efforts. Reduced clarity makes it very difficult or impossible to survey and find milfoil plants, and potentially toxic bloom conditions prevent the SCUBA team that manually removes the milfoil plants from entering the water.

What are 30 Mile and ALIC doing about it?

While we continue to study the lake to better understand why the lake has bloomed in recent years, 30 Mile and ALIC have made great strides towards addressing phosphorus loading from the watershed. Before we could apply for federal grant funding to help pay for the cost of this work, we first had to complete a watershed survey and develop an approved watershed-based protection plan that provided a road map for remediation work over the next 10 years. The watershed survey was completed in May 2022 and our full report and 2-page summary are available online: https://30mileriver.org/watershed-surveys/

The Androscoggin Lake Watershed-Based Protection Plan (WBPP) was accepted by the US EPA and the Maine DEP in early 2023. Using information collected during the watershed survey, 30 Mile developed this plan during the winter of ’22-’23. With assistance from ALIC, Maine DEP, and US EPA, the plan lays out a strategy for watershed mitigation and water quality protection efforts over the next 10 years. This also means we are now eligible to apply for federal Clean Water Act funding for the next 10 years.

In August of 2023, 30 Mile was awarded a grant for the Androscoggin Lake Watershed Protection Project, Phase I (Clean Water Act Section 319 grant). This much-needed project brings $149,730 of grant funding to the Androscoggin Lake watershed over the next three years. The grant will largely support construction costs associated with improvements to town roads, private roads, and other public and private property. All these efforts aim to reduce erosion and phosphorus loading to the lake in order to reduce the frequency of future algal blooms.

In May 2023, 30 Mile’s application to the Maine Outdoor Heritage Fund for an additional project was awarded funding, and completed in 2024. This project includes the completion of a Septic System Risk Analysis and Septic System database for the entire 30 Mile River Watershed. It is an ongoing effort to continue expanding the use of this resource, including in partnership with towns and to be used as a resource for the public.

In 2024 and 2025, we continued our advanced water quality monitoring throughout the season. ALIC continued to conduct LakeSmart visits, and 30 Mile supported both planning and implementation of erosion control projects funded by the 319 grant.

In 2025, 30 Mile and Maine DEP staff collected additional bloom samples to test for toxicity and algal species. In partnership with ALIC, 30 Mile hosted a Septic Social, aimed at educating the public on the importance of regular septic system maintenance. Throughout the summer, the US EPA made multiple visits to the lake, collecting data to create a bathymetric map. This map will provide 30 Mile with essential updated data to be used for calculations of lake depths and water volume to better understand the lake, and to identify locations for sediment samples to be collected in 2026.

Additionally, 30 Mile received recommendations from a consulting lake scientist for the final steps needed to complete the data collection and analysis necessary to determine what is causing the recurring blooms, and how we can manage them in the future. This is an ongoing process, with continued communication between lake experts, Maine DEP, and other resources.

What can I do NOW to help?

    • Donate to 30 Mile to support our water quality monitoring program and our work to address this problem: https://30mileriver.org/ways-to-give/
    • Become a member of the Androscoggin Lake Improvement Corporation (ALIC) https://androscogginlake.org/alic/how-to-help/donate/   
    • Be an advocate for lake protection at the town level. Local select boards, planning boards, and code enforcement officers all make decisions that can impact the lake. 
    • Share this information with your friends, family and neighbors. Be an ambassador for the lake!
    • Address erosion on your property. Exposed soil delivers phosphorus to the lake each time it rains. Phosphorus feeds algae in the lake!
    • If you are a landowner with an erosion site identified during the 2022 watershed survey, contact 30 Mile to see what cost-sharing opportunities are available to help implement your project!
    • Establish or improve the vegetation on your shoreline. The bigger (wider) your shoreline buffer, the better it is for Androscoggin Lake.
    • Do you live on a camp road? Gravel roads can be a huge polluter of the lake when sediment and pollutants from the road flow into streams and lakes during rain events. Be sure that your road isn’t part of the problem. Contact 30 Mile for technical assistance and learn more about how to maintain your road and protect the lake: https://www.maine.gov/dep/land/watershed/camp/road/gravel_road_manual.pdf  
    • Become LakeSmart! Contact ALIC’s LakeSmart team to receive a FREE property visit to learn more about how you can improve your property for the benefit of Androscoggin Lake. Visit https://www.lakes.me/lakesmart to learn more about this fantastic statewide program!
    • Stop using fertilizers on your lakefront properties
    • Maintain a healthy septic system, and pump your septic tank regularly. Visit https://30mileriver.org/septic-system-vulnerability-study/ to learn more about proper septic maintenance and go through our questionnaire to learn what else you can do to properly maintain your system. 
    • Volunteer. Help support water quality monitoring and LakeSmart. Sign up here: https://30mileriver.org/volunteer/ 

    Learn more about how you can reduce your impact by visiting Maine DEP’s website for Shorefront Property Owners: https://www.maine.gov/dep/land/watershed/camp/index.html or Maine Lake’s Lake Library: https://www.lakes.me/library.

Where can I learn more information?

Algal Blooms in Maine Lakes (Maine DEP): https://www.maine.gov/dep/water/lakes/algalbloom.html 

Cyanobacteria and Toxins (Maine DEP): https://www.maine.gov/dep/water/lakes/cyanobacteria.html   

Most recent water quality data and reports (30 Mile): https://30mileriver.org/androscoggin-lake/ 

Most recent information about blooms in Androscoggin Lake, and what 30 Mile and ALIC are doing in response: https://30mileriver.org/androscoggin-bloom/ 

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