Is Longley Pond safe to swim?

As of July 22, 2026, Longley Pond in Piscataquis County, Maine carries a swim caution. Satellite imagery measured 41,094 cells/mL of blue-green algae on July 21, 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

Longley Pond is a pond in Piscataquis County, Maine covering about 1.2 sq mi, the 179th-largest of the 319 lakes SwimZone monitors in Maine. Satellite imagery measured 41,094 cells/mL of blue-green algae on July 21, 2026, elevated but below 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, Longley Pond has reached blue-green algae advisory levels in 1 of them, most recently in September 2025. Blooms here have been occasional rather than annual. Its highest recorded reading was 190,135 cells/mL in September 2025.

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 Longley Pond right now?

Longley Pond carries a swim caution today. Satellite imagery measured 41,094 cells/mL of blue-green algae on July 21, 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 Longley Pond have blue-green algae (cyanobacteria)?

Low levels. Satellite monitoring measured 41,094 cells/mL at Longley Pond on July 21, 2026, below the 100,000 cells/mL advisory threshold. Keep an eye out for surface scum, which can concentrate quickly.

Can dogs swim in Longley Pond?

Use caution. Blue-green algae at Longley Pond are elevated (41,094 cells/mL on July 21, 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 Longley Pond have blue-green algae blooms?

Over 7 summers of satellite monitoring since 2020, Longley Pond has reached blue-green algae advisory levels in 1 of them, most recently in September 2025. Blooms here have been occasional rather than annual. Its highest recorded reading was 190,135 cells/mL in September 2025.

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 Longley Pond'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 Longley Pond, 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?→