Is Flagstaff Lake safe to swim?

As of July 22, 2026, Flagstaff Lake in Somerset County, Maine is clear to swim. Satellite imagery detected no blue-green algae bloom as of July 21, 2026. Rainfall over the past week totaled 0.0 in, which can wash bacteria and nutrients into the water.

How this read is built

Flagstaff Lake is a lake in Somerset County, Maine covering about 27.2 sq mi, the 5th-largest of the 319 lakes SwimZone monitors in Maine. Satellite imagery detected no blue-green algae bloom as of July 21, 2026. 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, Flagstaff Lake has reached blue-green algae advisory levels in 2 of them, most recently in September 2021. Blooms here have been occasional rather than annual. Its highest recorded reading was 574,835 cells/mL in September 2020.

Is it safe to swim in Flagstaff Lake right now?

Flagstaff Lake is clear to swim today. Satellite imagery detected no blue-green algae bloom as of July 21, 2026. Conditions can change quickly with wind, heat, and rain, so check the posted signs and look at the water before you get in.

Does Flagstaff Lake have blue-green algae (cyanobacteria)?

No blue-green algae bloom is detectable at Flagstaff Lake as of July 21, 2026 (below the satellite's roughly 10,000 cells/mL detection limit). Cyanobacteria can still appear within hours in warm, calm, nutrient-rich water, so look before you swim.

Can dogs swim in Flagstaff Lake?

No bloom is detected at Flagstaff Lake today, but dogs are much more vulnerable to blue-green algae than people, and blooms can form within hours. Always keep dogs away from water that looks green, scummy, or discolored, and rinse them off after swimming.

How often does Flagstaff Lake have blue-green algae blooms?

Over 7 summers of satellite monitoring since 2020, Flagstaff Lake has reached blue-green algae advisory levels in 2 of them, most recently in September 2021. Blooms here have been occasional rather than annual. Its highest recorded reading was 574,835 cells/mL in September 2020.

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 Flagstaff 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 Flagstaff Lake, and a recent-rainfall overlay, all refreshed daily. It was last updated July 22, 2026.