Is South Fork Reservoir safe to swim?

As of July 20, 2026, South Fork Reservoir in Elko County, Nevada carries a swim caution. Satellite imagery measured 88,394 cells/mL of blue-green algae on July 19, 2026, elevated but below 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

South Fork Reservoir is a reservoir in Elko County, Nevada. Satellite imagery measured 88,394 cells/mL of blue-green algae on July 19, 2026, elevated but below 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, South Fork Reservoir has reached blue-green algae advisory levels in 6 of them, most recently in August 2025. This is a lake that blooms most summers. Its highest recorded reading was 2,307,932 cells/mL in September 2024.

Is it safe to swim in South Fork Reservoir right now?

South Fork Reservoir carries a swim caution today. Satellite imagery measured 88,394 cells/mL of blue-green algae on July 19, 2026, elevated but below 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 South Fork Reservoir have blue-green algae (cyanobacteria)?

Low levels. Satellite monitoring measured 88,394 cells/mL at South Fork Reservoir on July 19, 2026, below the 100,000 cells/mL advisory threshold. Keep an eye out for surface scum, which can concentrate quickly.

Can dogs swim in South Fork Reservoir?

Use caution. Blue-green algae at South Fork Reservoir are elevated (88,394 cells/mL on July 19, 2026). Dogs are far more sensitive to cyanobacteria than people, so keep them out of the water and away from surface scum.

How often does South Fork Reservoir have blue-green algae blooms?

Over 7 summers of satellite monitoring since 2020, South Fork Reservoir has reached blue-green algae advisory levels in 6 of them, most recently in August 2025. This is a lake that blooms most summers. Its highest recorded reading was 2,307,932 cells/mL in September 2024.

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 South Fork 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 South Fork Reservoir, and a recent-rainfall overlay, all refreshed daily. It was last updated July 20, 2026.