Is Fifth Musquacook Lake safe to swim?

As of July 22, 2026, Fifth Musquacook Lake in Piscataquis County, Maine is not recommended for swimming. Satellite imagery measured 1,272,047 cells/mL of blue-green algae on July 21, 2026, above the 100,000 cells/mL advisory threshold. Rainfall over the past week totaled 1.1 in, which can wash bacteria and nutrients into the water.

How this read is built

Fifth Musquacook Lake is a lake in Piscataquis County, Maine covering about 0.7 sq mi, the 257th-largest of the 319 lakes SwimZone monitors in Maine. Satellite imagery measured 1,272,047 cells/mL of blue-green algae on July 21, 2026, above the 100,000 cells/mL advisory threshold.

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, Fifth Musquacook Lake has reached blue-green algae advisory levels in 7 of them, most recently in July 2026. This is a lake that blooms most summers. Its highest recorded reading was 1,642,037 cells/mL in July 2020.

It is currently peak season for blue-green algae, when warm, calm water lets blooms form fastest. This lake has bloomed in most monitored summers (7 of 7), historically peaking around July. 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 Fifth Musquacook Lake right now?

Fifth Musquacook Lake is not recommended for swimming today. Satellite imagery measured 1,272,047 cells/mL of blue-green algae on July 21, 2026, above 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 Fifth Musquacook Lake have blue-green algae (cyanobacteria)?

Yes. Satellite monitoring measured 1,272,047 cells/mL of blue-green algae (cyanobacteria) at Fifth Musquacook Lake on July 21, 2026, above the 100,000 cells/mL advisory level. Avoid swimming and keep children and pets out of the water.

Can dogs swim in Fifth Musquacook Lake?

No. Blue-green algae at Fifth Musquacook Lake is above the safe-contact threshold (1,272,047 cells/mL on July 21, 2026). Cyanobacteria toxins can be rapidly fatal to dogs, which swallow it while swimming and lick it from their fur. Keep dogs out of the water and away from any scum along the shore.

How often does Fifth Musquacook Lake have blue-green algae blooms?

Over 7 summers of satellite monitoring since 2020, Fifth Musquacook Lake has reached blue-green algae advisory levels in 7 of them, most recently in July 2026. This is a lake that blooms most summers. Its highest recorded reading was 1,642,037 cells/mL in July 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 Fifth Musquacook 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 Fifth Musquacook 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?→