Is Lake Overholser safe to swim?

As of July 20, 2026, Lake Overholser in Canadian County, Oklahoma is not recommended for swimming. Satellite imagery measured 1,135,594 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 Overholser is a lake in Canadian County, Oklahoma covering about 2.5 sq mi, the 32nd-largest of the 57 lakes SwimZone monitors in Oklahoma. Satellite imagery measured 1,135,594 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 Overholser 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 2,119,644 cells/mL in June 2023.

Is it safe to swim in Lake Overholser right now?

Lake Overholser is not recommended for swimming today. Satellite imagery measured 1,135,594 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 Overholser have blue-green algae (cyanobacteria)?

Yes. Satellite monitoring measured 1,135,594 cells/mL of blue-green algae (cyanobacteria) at Lake Overholser 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 Overholser?

No. Blue-green algae at Lake Overholser is above the safe-contact threshold (1,135,594 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 Overholser have blue-green algae blooms?

Over 7 summers of satellite monitoring since 2020, Lake Overholser 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 2,119,644 cells/mL in June 2023.

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