Is Copan Lake safe to swim?

As of July 20, 2026, Copan Lake in Washington County, Oklahoma is not recommended for swimming. Satellite imagery measured 238,574 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

Copan Lake is a lake in Washington County, Oklahoma covering about 6.3 sq mi, the 23rd-largest of the 57 lakes SwimZone monitors in Oklahoma. Satellite imagery measured 238,574 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, Copan Lake has reached blue-green algae advisory levels in 3 of them, most recently in August 2024. Its highest recorded reading was 785,350 cells/mL in September 2020.

Is it safe to swim in Copan Lake right now?

Copan Lake is not recommended for swimming today. Satellite imagery measured 238,574 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 Copan Lake have blue-green algae (cyanobacteria)?

Yes. Satellite monitoring measured 238,574 cells/mL of blue-green algae (cyanobacteria) at Copan 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 Copan Lake?

No. Blue-green algae at Copan Lake is above the safe-contact threshold (238,574 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 Copan Lake have blue-green algae blooms?

Over 7 summers of satellite monitoring since 2020, Copan Lake has reached blue-green algae advisory levels in 3 of them, most recently in August 2024. Its highest recorded reading was 785,350 cells/mL in September 2020.

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

Today, 22 Oklahoma waters are above a safe-contact threshold and 2 more warrant caution, out of 64 monitored waters SwimZone tracks in the state.

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