Is Bromley Lake safe to swim?

As of July 20, 2026, Bromley Lake in McHenry County, North Dakota is clear to swim. Satellite imagery measured 19,105 cells/mL of blue-green algae on July 19, 2026, well below the 100,000 cells/mL advisory threshold. Rainfall over the past week totaled 0.0 in, which can wash bacteria and nutrients into the water.

How this read is built

Bromley Lake is a lake in McHenry County, North Dakota covering about 0.5 sq mi, the 195th-largest of the 216 lakes SwimZone monitors in North Dakota. Satellite imagery measured 19,105 cells/mL of blue-green algae on July 19, 2026, well below 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, Bromley Lake has reached blue-green algae advisory levels in 4 of them, most recently in July 2026. Its highest recorded reading was 1,689,285 cells/mL in August 2022.

Is it safe to swim in Bromley Lake right now?

Bromley Lake is clear to swim today. Satellite imagery measured 19,105 cells/mL of blue-green algae on July 19, 2026, well below 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 Bromley Lake have blue-green algae (cyanobacteria)?

Low levels. Satellite monitoring measured 19,105 cells/mL at Bromley Lake on July 19, 2026, below the 100,000 cells/mL advisory threshold. Keep an eye out for surface scum, which can concentrate quickly.

Can dogs swim in Bromley Lake?

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

Over 7 summers of satellite monitoring since 2020, Bromley Lake has reached blue-green algae advisory levels in 4 of them, most recently in July 2026. Its highest recorded reading was 1,689,285 cells/mL in August 2022.

How many North Dakota lakes and beaches are unsafe for swimming today?

Today, 167 North Dakota waters are above a safe-contact threshold and 4 more warrant caution, out of 241 monitored waters SwimZone tracks in the state.

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