Is Coldwater Lake safe to swim?

As of July 20, 2026, Coldwater Lake in McIntosh County, North Dakota is clear to swim. Satellite imagery detected no blue-green algae bloom as of July 19, 2026. Rainfall over the past week totaled 0.4 in, which can wash bacteria and nutrients into the water.

How this read is built

Coldwater Lake is a lake in McIntosh County, North Dakota covering about 0.5 sq mi, the 191st-largest of the 216 lakes SwimZone monitors in North Dakota. 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, Coldwater Lake has reached blue-green algae advisory levels in 3 of them, most recently in July 2022. Its highest recorded reading was 1,508,075 cells/mL in July 2020.

Is it safe to swim in Coldwater Lake right now?

Coldwater Lake 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 Coldwater Lake have blue-green algae (cyanobacteria)?

No blue-green algae bloom is detectable at Coldwater Lake 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 Coldwater Lake?

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

Over 7 summers of satellite monitoring since 2020, Coldwater Lake has reached blue-green algae advisory levels in 3 of them, most recently in July 2022. Its highest recorded reading was 1,508,075 cells/mL in July 2020.

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 Coldwater 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 Coldwater Lake, and a recent-rainfall overlay, all refreshed daily. It was last updated July 20, 2026.