Is Atkinson Lake safe to swim?

As of July 20, 2026, Atkinson Lake in St. Clair County, Missouri is not recommended for swimming. Satellite imagery measured 1,272,047 cells/mL of blue-green algae on July 19, 2026, above the 100,000 cells/mL advisory threshold. Rainfall over the past week totaled 0.1 in, which can wash bacteria and nutrients into the water.

How this read is built

Atkinson Lake is a lake in St. Clair County, Missouri covering about 0.7 sq mi, the 18th-largest of the 32 lakes SwimZone monitors in Missouri. Satellite imagery measured 1,272,047 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, Atkinson 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 1,892,270 cells/mL in July 2026.

Is it safe to swim in Atkinson Lake right now?

Atkinson Lake is not recommended for swimming today. Satellite imagery measured 1,272,047 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 Atkinson Lake have blue-green algae (cyanobacteria)?

Yes. Satellite monitoring measured 1,272,047 cells/mL of blue-green algae (cyanobacteria) at Atkinson Lake 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 Atkinson Lake?

No. Blue-green algae at Atkinson Lake is above the safe-contact threshold (1,272,047 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 Atkinson Lake have blue-green algae blooms?

Over 7 summers of satellite monitoring since 2020, Atkinson 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 1,892,270 cells/mL in July 2026.

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

Today, 14 Missouri waters are above a safe-contact threshold and 1 more warrant caution, out of 34 monitored waters SwimZone tracks in the state.

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