Damariscotta Lake Water Quality
Update - Summer 2026: Water quality monitoring on Damariscotta Lake has resumed for the 2026 season. Regular updates are posted to Damariscotta Lake Watch on Facebook and Instagram and the Swim Guide for the latest updates.
Links below go directly to the Swim Guide listings for testing locations:
Open water swimming has inherent risks, but best practices are to avoid dense or scummy areas, avoid inadvertently swallowing lake water, keep pets from drinking lake water or licking fur with scum on it, avoid using lake water for household use and drinking, and shower and wash swimsuits after swimming.
Additional information about cyanobacteria can be found on the state’s webpage.
Frequently Asked Questions (FAQ)
What is cyanobacteria? Cyanobacteria (often called blue-green algae) are aquatic bacteria that photosynthesize and have been around for over 3.5 billion years. When conditions are right their numbers can explode causing what we call a “bloom”. Cyanobacteria blooms can present as paint-like smears in the lake or simply turn the water green. Additionally, cyanobacteria are able to regulate their position in the water column so the density can appear to change throughout the day and be different day to day.
Is it toxic?The species of cyanobacteria that Damariscotta Lake typically has issues with do not produce the most common form of cyanotoxins. However, we are encouraging people to be cautious. Degree of exposure is important, the more contact with the cyanobacteria the more potential for toxicity. This can be because of high density of cyanobacteria or prolonged exposure. Avoid areas of high concentration such as scum lines along the shoreline in windy conditions. Do not allow children to play in those areas, do not ingest this water nor allow your pets to drink this water, and shower after swimming. You should not use your lake intake for drinking water as reverse osmosis and boiling do not remove cyanotoxins. Use bottled water for drinking and take quick showers as cyanotoxins can become aerosolized and cause health problems. .
What causes cyanobacteria problems? High air and water temperatures combined with excess nutrients (primarily phosphorus) create ideal conditions for algae and cyanobacteria growth. There are multiple ways phosphorus enters a lake, including erosion, fertilizers, septic systems, agricultural sources, and others.
Signs and symptoms of exposure:nausea, vomiting, diarrhea.
What can I do?
Reduce soil erosion by seeding and mulching bare areas
Maintain a ribbon of woody vegetation between your property and the lake
Direct water from roofs, driveways and roads to stable vegetated areas
Eliminate the use of fertilizer on lakefront property
Regularly maintain your septic system (contact your local septic service to have your system maintained)
Consider getting your property certified as Lake Smart.
Avoid creating a wake as much as possible in the very narrow South Arm. Erosion is reduced if wakes are generated at least 500 feet from shore.
Volunteer0in your community. Midcoast Conservancy has opportunities for Invasive Plant Patrol, among others
Donateto support our work to protect and restore Damariscotta Lake - THANK YOU!