Is Sherman Reservoir safe to swim?

As of July 20, 2026, Sherman Reservoir in Sherman County, Nebraska is not recommended for swimming. Satellite imagery measured 104,796 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

Sherman Reservoir is a reservoir in Sherman County, Nebraska. Satellite imagery measured 104,796 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, Sherman Reservoir has not reached a blue-green algae advisory level. Conditions can still change quickly, so check the current read before you swim.

Is it safe to swim in Sherman Reservoir right now?

Sherman Reservoir is not recommended for swimming today. Satellite imagery measured 104,796 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 Sherman Reservoir have blue-green algae (cyanobacteria)?

Yes. Satellite monitoring measured 104,796 cells/mL of blue-green algae (cyanobacteria) at Sherman 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 Sherman Reservoir?

No. Blue-green algae at Sherman Reservoir is above the safe-contact threshold (104,796 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 Sherman Reservoir have blue-green algae blooms?

Over 7 summers of satellite monitoring since 2020, Sherman Reservoir has not reached a blue-green algae advisory level. Conditions can still change quickly, so check the current read before you swim.

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

Today, 44 Nebraska waters are above a safe-contact threshold and 4 more warrant caution, out of 83 monitored waters SwimZone tracks in the state.

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