Androscoggin Lake Bloom FAQ’s

September 18, 2023

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 nuisance lake-wide algal blooms two out of the last three years, it is still considered a fairly infrequent bloomer, with only three years with documented lake-wide algal blooms in the near 50-year historical monitoring record. Since 2022, we have been studying the lake much  more thoroughly to better understand what is causing the bloom. 

What makes the water green?

Algae, known as cyanobacteria. Originally called blue-green algae because dense blooms 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 (phosphorus) concentrations 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 have 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.

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

Where can I donate to support this work?

Learn more and DONATE to the ‘Save Androscoggin’ campaign that helps provide the resources we need over the next three years to work toward eradicating invasive milfoil and reducing the chance of recurring algae blooms: 

Does it affect wildlife?

In the case of a severe bloom that is producing toxins, there is potential that fish and other wildlife like loons can be negatively affected by high levels of toxins if they consume the water and or algae directly, or have consumed other organisms that have consumed the water or algae. 

Algal blooms in general can exacerbate problems with low oxygen levels in lakes, which can be detrimental to fish and other aquatic organisms who 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 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 important 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 Androscoggin Lake’s 2022 Water Quality Report here:

Does this relate to the milfoil problem?

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 2021 and 2023 created a challenge for late-season management of the milfoil infestation and removal efforts. Reduced clarity makes it very difficult to 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 the full report or 2-page summary is available online: 

The Androscoggin Lake Watershed-Based Protection Plan (WBPP) was accepted by US EPA and ME 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 two 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 is now underway. This project includes the completion of a Septic System Risk Analysis and Septic System database for the entire 30 Mile River Watershed. Completion of this project is expected in Spring 2024.

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:
    • Become a member of the Androscoggin Lake Improvement Corporation (ALIC)  
    • Be an advocate for lake protection at the town level. Local select boards, planning boards, and code enforcements 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, if water that hits the surface picks up sediment and flows to the lake. 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:  
    • Become LakeSmart! Contact ALIC’s LakeSmart team to receive a FREE evaluation and learn more about how you can improve your property for the benefit of Androscoggin Lake. Request an evaluation by emailing, and visit to learn more about this fantastic program!
    • Stop using fertilizers on your lakefront properties
    • Maintain a healthy septic system, and pump your septic tank regularly.
    • Volunteer. Help support water quality monitoring and LakeSmart. Sign up here: 
    • Learn more about how you can reduce your impact by visiting Maine DEP’s website for Shorefront Property Owners: or Maine Lake’s Lake Library:

Where can I learn more information?

Algal Blooms in Maine Lakes (Maine DEP): 

Cyanobacteria and Toxins (Maine DEP):   

Most recent water quality data and reports (30 Mile): 

Most recent information about blooms in Androscoggin Lake, and what 30 Mile and ALIC are doing in response: