Is Lahontan Reservoir safe to swim?

As of July 20, 2026, Lahontan Reservoir in Lyon County, Nevada is not recommended for swimming. Satellite imagery measured 445,311 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

Lahontan Reservoir is a reservoir in Lyon County, Nevada covering about 15.6 sq mi, the 6th-largest of the 47 lakes SwimZone monitors in Nevada. Satellite imagery measured 445,311 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, Lahontan Reservoir 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 2,374,340 cells/mL in July 2025.

Is it safe to swim in Lahontan Reservoir right now?

Lahontan Reservoir is not recommended for swimming today. Satellite imagery measured 445,311 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 Lahontan Reservoir have blue-green algae (cyanobacteria)?

Yes. Satellite monitoring measured 445,311 cells/mL of blue-green algae (cyanobacteria) at Lahontan Reservoir 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 Lahontan Reservoir?

No. Blue-green algae at Lahontan Reservoir is above the safe-contact threshold (445,311 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 Lahontan Reservoir have blue-green algae blooms?

Over 7 summers of satellite monitoring since 2020, Lahontan Reservoir 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 2,374,340 cells/mL in July 2025.

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

Today, 13 Nevada waters are above a safe-contact threshold and 1 more warrant caution, out of 50 monitored waters SwimZone tracks in the state.

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