Is Lake Saint Helen safe to swim?

As of July 20, 2026, Lake Saint Helen in Roscommon County, Michigan is not recommended for swimming. Satellite imagery measured 110,913 cells/mL of blue-green algae on July 19, 2026, above the 100,000 cells/mL advisory threshold. Rainfall over the past week totaled 0.0 in, which can wash bacteria and nutrients into the water.

How this read is built

Lake Saint Helen is a lake in Roscommon County, Michigan covering about 3.8 sq mi, the 35th-largest of the 263 lakes SwimZone monitors in Michigan. Satellite imagery measured 110,913 cells/mL of blue-green algae on July 19, 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, Lake Saint Helen has reached blue-green algae advisory levels in 4 of them, most recently in September 2024. Its highest recorded reading was 432,856 cells/mL in August 2023.

Is it safe to swim in Lake Saint Helen right now?

Lake Saint Helen is not recommended for swimming today. Satellite imagery measured 110,913 cells/mL of blue-green algae on July 19, 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 Lake Saint Helen have blue-green algae (cyanobacteria)?

Yes. Satellite monitoring measured 110,913 cells/mL of blue-green algae (cyanobacteria) at Lake Saint Helen on July 19, 2026, above the 100,000 cells/mL advisory level. Avoid swimming and keep children and pets out of the water.

Can dogs swim in Lake Saint Helen?

No. Blue-green algae at Lake Saint Helen is above the safe-contact threshold (110,913 cells/mL on July 19, 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 Lake Saint Helen have blue-green algae blooms?

Over 7 summers of satellite monitoring since 2020, Lake Saint Helen has reached blue-green algae advisory levels in 4 of them, most recently in September 2024. Its highest recorded reading was 432,856 cells/mL in August 2023.

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

Today, 47 Michigan waters are above a safe-contact threshold and 100 more warrant caution, out of 882 monitored waters SwimZone tracks in the state.

How is Lake Saint Helen'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 Lake Saint Helen, and a recent-rainfall overlay, all refreshed daily. It was last updated July 20, 2026.