Is Shallow Lake safe to swim?

As of July 20, 2026, Shallow Lake in Harney County, Oregon is not recommended for swimming. Satellite imagery measured 307,966 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

Shallow Lake is a lake in Harney County, Oregon covering about 3.6 sq mi, the 34th-largest of the 115 lakes SwimZone monitors in Oregon. Satellite imagery measured 307,966 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, Shallow Lake has reached blue-green algae advisory levels in 7 of them, most recently in June 2026. This is a lake that blooms most summers. Its highest recorded reading was 1,013,778 cells/mL in September 2020.

Is it safe to swim in Shallow Lake right now?

Shallow Lake is not recommended for swimming today. Satellite imagery measured 307,966 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 Shallow Lake have blue-green algae (cyanobacteria)?

Yes. Satellite monitoring measured 307,966 cells/mL of blue-green algae (cyanobacteria) at Shallow Lake 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 Shallow Lake?

No. Blue-green algae at Shallow Lake is above the safe-contact threshold (307,966 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 Shallow Lake have blue-green algae blooms?

Over 7 summers of satellite monitoring since 2020, Shallow Lake has reached blue-green algae advisory levels in 7 of them, most recently in June 2026. This is a lake that blooms most summers. Its highest recorded reading was 1,013,778 cells/mL in September 2020.

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

Today, 31 Oregon waters are above a safe-contact threshold and 1 more warrant caution, out of 213 monitored waters SwimZone tracks in the state.

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