Is Ferguson Reservoir safe to swim?

As of July 22, 2026, Ferguson Reservoir in Allen County, Ohio is not recommended for swimming. Satellite imagery measured 558,757 cells/mL of blue-green algae on July 19, 2026, above the 100,000 cells/mL advisory threshold. Rainfall over the past week totaled 0.3 in, which can wash bacteria and nutrients into the water.

How this read is built

Ferguson Reservoir is a reservoir in Allen County, Ohio covering about 0.5 sq mi, the 40th-largest of the 41 lakes SwimZone monitors in Ohio. Satellite imagery measured 558,757 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, Ferguson Reservoir has reached blue-green algae advisory levels in 6 of them, most recently in August 2025. This is a lake that blooms most summers. Its highest recorded reading was 1,308,648 cells/mL in September 2020.

It is currently peak season for blue-green algae, when warm, calm water lets blooms form fastest. This lake has bloomed in most monitored summers (6 of 7), historically peaking around September. Early summer, before the water fully warms, has generally been the safer window here; check the current read before you go either way.

Is it safe to swim in Ferguson Reservoir right now?

Ferguson Reservoir is not recommended for swimming today. Satellite imagery measured 558,757 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 Ferguson Reservoir have blue-green algae (cyanobacteria)?

Yes. Satellite monitoring measured 558,757 cells/mL of blue-green algae (cyanobacteria) at Ferguson Reservoir 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 Ferguson Reservoir?

No. Blue-green algae at Ferguson Reservoir is above the safe-contact threshold (558,757 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 Ferguson Reservoir have blue-green algae blooms?

Over 7 summers of satellite monitoring since 2020, Ferguson Reservoir has reached blue-green algae advisory levels in 6 of them, most recently in August 2025. This is a lake that blooms most summers. Its highest recorded reading was 1,308,648 cells/mL in September 2020.

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

Today, 33 Ohio waters are above a safe-contact threshold and 32 more warrant caution, out of 101 monitored waters SwimZone tracks in the state.

How is Ferguson 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 Ferguson Reservoir, and a recent-rainfall overlay, all refreshed daily. It was last updated July 22, 2026.

• Blue-green algae and dogs→
• What does blue-green algae look like?→
• When is algae season?→