Is Great Moose Lake safe to swim?

As of July 22, 2026, Great Moose Lake in Somerset County, Maine carries a swim caution. Satellite imagery measured 23,972 cells/mL of blue-green algae on July 18, 2026, elevated but below the 100,000 cells/mL advisory threshold. Rainfall over the past week totaled 0.1 in, which can wash bacteria and nutrients into the water.

How this read is built

Great Moose Lake is a lake in Somerset County, Maine covering about 6 sq mi, the 40th-largest of the 319 lakes SwimZone monitors in Maine. Satellite imagery measured 23,972 cells/mL of blue-green algae on July 18, 2026, elevated but below the 100,000 cells/mL advisory threshold. Larger, warmer waters like this can hold a bloom for weeks once nutrients and calm weather line up.

Blue-green algae (cyanobacteria) blooms are most common from midsummer into early fall, when the water is warm, calm, and rich in nutrients from runoff. They can produce toxins that make people sick and can be rapidly fatal to dogs, so skip water that looks green, scummy, or like spilled paint, and keep children and pets out of it.

Over 7 summers of satellite monitoring since 2020, Great Moose Lake has reached blue-green algae advisory levels in 1 of them, most recently in September 2024. Blooms here have been occasional rather than annual. Its highest recorded reading was 375,615 cells/mL in September 2024.

It is currently peak season for blue-green algae, when warm, calm water lets blooms form fastest. This lake has bloomed in 1 of 7 monitored summers, historically peaking around September. Early summer, before the water fully warms, has generally been the safer window here; check the current read before you go either way.

Is it safe to swim in Great Moose Lake right now?

Great Moose Lake carries a swim caution today. Satellite imagery measured 23,972 cells/mL of blue-green algae on July 18, 2026, elevated but below the 100,000 cells/mL advisory threshold. Conditions can change quickly with wind, heat, and rain, so check the posted signs and look at the water before you get in.

Does Great Moose Lake have blue-green algae (cyanobacteria)?

Low levels. Satellite monitoring measured 23,972 cells/mL at Great Moose Lake on July 18, 2026, below the 100,000 cells/mL advisory threshold. Keep an eye out for surface scum, which can concentrate quickly.

Can dogs swim in Great Moose Lake?

Use caution. Blue-green algae at Great Moose Lake are elevated (23,972 cells/mL on July 18, 2026). Dogs are far more sensitive to cyanobacteria than people, so keep them out of the water and away from surface scum.

How often does Great Moose Lake have blue-green algae blooms?

Over 7 summers of satellite monitoring since 2020, Great Moose Lake has reached blue-green algae advisory levels in 1 of them, most recently in September 2024. Blooms here have been occasional rather than annual. Its highest recorded reading was 375,615 cells/mL in September 2024.

How many Maine lakes and beaches are unsafe for swimming today?

Today, 15 Maine waters are above a safe-contact threshold and 33 more warrant caution, out of 457 monitored waters SwimZone tracks in the state.

How is Great Moose Lake's water quality measured?

SwimZone builds this read from EPA CyAN satellite imagery for blue-green algae, official beach and fecal-bacteria advisories where a program monitors Great Moose Lake, and a recent-rainfall overlay, all refreshed daily. It was last updated July 22, 2026.

• Blue-green algae and dogs→
• What does blue-green algae look like?→
• When is algae season?→