Is Upper Lake Mary safe to swim?

As of July 20, 2026, Upper Lake Mary in Coconino County, Arizona is clear to swim. Satellite imagery detected no blue-green algae bloom as of July 19, 2026. Rainfall over the past week totaled 3.8 in, which can wash bacteria and nutrients into the water.

How this read is built

Upper Lake Mary is a lake in Coconino County, Arizona covering about 1.3 sq mi, the 11th-largest of the 21 lakes SwimZone monitors in Arizona. 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, Upper Lake Mary 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 Upper Lake Mary right now?

Upper Lake Mary 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 Upper Lake Mary have blue-green algae (cyanobacteria)?

No blue-green algae bloom is detectable at Upper Lake Mary 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 Upper Lake Mary?

No bloom is detected at Upper Lake Mary 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 Upper Lake Mary have blue-green algae blooms?

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

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

Today, 3 Arizona waters are above a safe-contact threshold and 1 more warrant caution, out of 22 monitored waters SwimZone tracks in the state.

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