Is Lake Hefner safe to swim?

As of July 20, 2026, Lake Hefner in Oklahoma County, Oklahoma is not recommended for swimming. Satellite imagery measured 386,423 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 Hefner is a lake in Oklahoma County, Oklahoma covering about 3.9 sq mi, the 27th-largest of the 57 lakes SwimZone monitors in Oklahoma. Satellite imagery measured 386,423 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 Hefner has reached blue-green algae advisory levels in 6 of them, most recently in June 2026. This is a lake that blooms most summers. Its highest recorded reading was 1,892,270 cells/mL in June 2021.

Is it safe to swim in Lake Hefner right now?

Lake Hefner is not recommended for swimming today. Satellite imagery measured 386,423 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 Hefner have blue-green algae (cyanobacteria)?

Yes. Satellite monitoring measured 386,423 cells/mL of blue-green algae (cyanobacteria) at Lake Hefner 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 Hefner?

No. Blue-green algae at Lake Hefner is above the safe-contact threshold (386,423 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 Hefner have blue-green algae blooms?

Over 7 summers of satellite monitoring since 2020, Lake Hefner has reached blue-green algae advisory levels in 6 of them, most recently in June 2026. This is a lake that blooms most summers. Its highest recorded reading was 1,892,270 cells/mL in June 2021.

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