Is Perry Lake safe to swim?

As of July 20, 2026, Perry Lake in Jefferson County, Kansas is not recommended for swimming. Satellite imagery measured 408,981 cells/mL of blue-green algae on July 19, 2026, above the 100,000 cells/mL advisory threshold. Rainfall over the past week totaled 0.8 in, which can wash bacteria and nutrients into the water.

How this read is built

Perry Lake is a lake in Jefferson County, Kansas covering about 16.8 sq mi, the 3rd-largest of the 28 lakes SwimZone monitors in Kansas. Satellite imagery measured 408,981 cells/mL of blue-green algae on July 19, 2026, above the 100,000 cells/mL advisory threshold. 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, Perry Lake has reached blue-green algae advisory levels in 6 of them, most recently in July 2026. This is a lake that blooms most summers. Its highest recorded reading was 643,907 cells/mL in June 2020.

Is it safe to swim in Perry Lake right now?

Perry Lake is not recommended for swimming today. Satellite imagery measured 408,981 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 Perry Lake have blue-green algae (cyanobacteria)?

Yes. Satellite monitoring measured 408,981 cells/mL of blue-green algae (cyanobacteria) at Perry 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 Perry Lake?

No. Blue-green algae at Perry Lake is above the safe-contact threshold (408,981 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 Perry Lake have blue-green algae blooms?

Over 7 summers of satellite monitoring since 2020, Perry Lake has reached blue-green algae advisory levels in 6 of them, most recently in July 2026. This is a lake that blooms most summers. Its highest recorded reading was 643,907 cells/mL in June 2020.

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

Today, 10 Kansas waters are above a safe-contact threshold and 1 more warrant caution, out of 30 monitored waters SwimZone tracks in the state.

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