Is Big Sand Wash Reservoir safe to swim?

As of July 20, 2026, Big Sand Wash Reservoir in Duchesne County, Utah is clear to swim. Satellite imagery detected no blue-green algae bloom as of July 19, 2026. Rainfall over the past week totaled 0.0 in, which can wash bacteria and nutrients into the water.

How this read is built

Big Sand Wash Reservoir is a reservoir in Duchesne County, Utah covering about 0.9 sq mi, the 28th-largest of the 48 lakes SwimZone monitors in Utah. 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, Big Sand Wash 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 Big Sand Wash Reservoir right now?

Big Sand Wash 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 Big Sand Wash Reservoir have blue-green algae (cyanobacteria)?

No blue-green algae bloom is detectable at Big Sand Wash 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 Big Sand Wash Reservoir?

No bloom is detected at Big Sand Wash 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 Big Sand Wash Reservoir have blue-green algae blooms?

Over 7 summers of satellite monitoring since 2020, Big Sand Wash 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 Utah lakes and beaches are unsafe for swimming today?

Today, 7 Utah waters are above a safe-contact threshold and 0 more warrant caution, out of 53 monitored waters SwimZone tracks in the state.

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