Is Pond Number Four safe to swim?

As of July 20, 2026, Pond Number Four in Teton County, Montana is clear to swim. Satellite imagery detected no blue-green algae bloom as of July 19, 2026. Rainfall over the past week totaled 0.2 in, which can wash bacteria and nutrients into the water.

How this read is built

Pond Number Four is a pond in Teton County, Montana covering about 0.8 sq mi, the 83rd-largest of the 124 lakes SwimZone monitors in Montana. Satellite imagery detected no blue-green algae bloom as of July 19, 2026.

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, Pond Number Four has reached blue-green algae advisory levels in 6 of them, most recently in June 2025. This is a lake that blooms most summers. Its highest recorded reading was 2,002,733 cells/mL in September 2024.

Is it safe to swim in Pond Number Four right now?

Pond Number Four is clear to swim today. Satellite imagery detected no blue-green algae bloom as of July 19, 2026. Conditions can change quickly with wind, heat, and rain, so check the posted signs and look at the water before you get in.

Does Pond Number Four have blue-green algae (cyanobacteria)?

No blue-green algae bloom is detectable at Pond Number Four as of July 19, 2026 (below the satellite's roughly 10,000 cells/mL detection limit). Cyanobacteria can still appear within hours in warm, calm, nutrient-rich water, so look before you swim.

Can dogs swim in Pond Number Four?

No bloom is detected at Pond Number Four today, but dogs are much more vulnerable to blue-green algae than people, and blooms can form within hours. Always keep dogs away from water that looks green, scummy, or discolored, and rinse them off after swimming.

How often does Pond Number Four have blue-green algae blooms?

Over 7 summers of satellite monitoring since 2020, Pond Number Four has reached blue-green algae advisory levels in 6 of them, most recently in June 2025. This is a lake that blooms most summers. Its highest recorded reading was 2,002,733 cells/mL in September 2024.

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

Today, 19 Montana waters are above a safe-contact threshold and 2 more warrant caution, out of 135 monitored waters SwimZone tracks in the state.

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