Is Fontenelle Reservoir safe to swim?

As of July 20, 2026, Fontenelle Reservoir in Lincoln County, Wyoming is clear to swim. Satellite imagery detected no blue-green algae bloom as of July 19, 2026. Rainfall over the past week totaled 0.5 in, which can wash bacteria and nutrients into the water.

How this read is built

Fontenelle Reservoir is a reservoir in Lincoln County, Wyoming covering about 12.2 sq mi, the 8th-largest of the 67 lakes SwimZone monitors in Wyoming. Satellite imagery detected no blue-green algae bloom as of July 19, 2026. 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, Fontenelle Reservoir has reached blue-green algae advisory levels in 5 of them, most recently in September 2025. This is a lake that blooms most summers. Its highest recorded reading was 1,424,895 cells/mL in September 2025.

Is it safe to swim in Fontenelle Reservoir right now?

Fontenelle Reservoir 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 Fontenelle Reservoir have blue-green algae (cyanobacteria)?

No blue-green algae bloom is detectable at Fontenelle Reservoir 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 Fontenelle Reservoir?

No bloom is detected at Fontenelle Reservoir 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 Fontenelle Reservoir have blue-green algae blooms?

Over 7 summers of satellite monitoring since 2020, Fontenelle Reservoir has reached blue-green algae advisory levels in 5 of them, most recently in September 2025. This is a lake that blooms most summers. Its highest recorded reading was 1,424,895 cells/mL in September 2025.

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

Today, 7 Wyoming waters are above a safe-contact threshold and 1 more warrant caution, out of 74 monitored waters SwimZone tracks in the state.

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