A scummy accumulation of cyanobacteria Gloeotrichia and Dolichospermum in a cove of Great Pond, July 9, 2026

Algae Update July 2026

So far, the lakes have remained nice and clear during the latest heatwave, but we are starting to see a measurable increase in algae growth. Not all algae growth is a concern though, so below is some information to understand what you’re seeing in the water as we wade into the hottest time of year.

First, if you want to check whether you see cyanobacteria, you can capture an algae sample in a jar and store it in the dark. After a day, cyanobacteria will float on the surface, while the rest will settle on the bottom. Of course, you can always bring a sample to the 7 Lakes Alliance office in Belgrade or contact danielle.wain@7lakesalliance.org or matt.farragher@7lakesalliance.org.

Types of Algae

Cyanobacteria are the most common type of algae that grows excessively in the Belgrade Lakes. Also referred to as “blue-green algae”, cyanobacteria are colonial, single-celled microorganisms that can form lake-wide algae blooms when conditions are favorable, like hot air temperatures and an abundance of phosphorus (the key nutrient for all algae in our lakes). Cyanobacteria can release compounds that are toxic to humans and pets. Because of this, the Maine DEP refers to lake-wide blooms where water clarity drops below 2 meters (6.6 feet) as “harmful algae blooms”, or HABs. We regularly test algae scums for toxins each year, and while we have never had a positive test, we recommend using caution and common sense when looking to swim! Our recommendation is to avoid contact with the water if you cannot see your feet when entering the lake, and to stay out of dense scum accumulations. Particularly, keep children and pets out of scums, as they tend to swallow more water when they swim.

Gloeotrichia echinulata (“Gloeo”) is a type of cyanobacteria that shows up each summer on Great Pond, Long Pond, and sometimes Messalonskee Lake. Gloeo forms large (~2 mm) spherical colonies that you can see with your naked eyes with a faint ring around their edge. Usually confined to deep, clear lakes, Gloeo emerges from the sediment and rises to the surface where it can spread horizontally across the entire lake. Gloeo can accumulate in coves and create thick scums.

Dolichospermum (“Doli”) is another common culprit of our lake-wide algae blooms, most recently on North Pond in 2024. Doli, along with other common cyanobacteria like microcystis, aphanizomenon, woronichinia (and more!) occur in all of our lakes each summer, but not usually in high abundances, unless conditions are favorable.

Other Algae Accumulations

It is very common to see patches of algae floating around in otherwise very clear areas. These masses are often a type of filamentous green algae which grows in shallow, vegetated areas of lakes that can break loose or accumulate into larger mats. While they might pick up other detritus along the way and can sometimes look unappealing, they are generally not a concern, unlike a lake-wide algae bloom or scum accumulations in a cove.

For more information, please contact Lake Scientist Matt Farragher or visit 7 Lakes Alliance at 137 Main St., Belgrade ME.