Is Black Lake safe to swim?

As of July 20, 2026, Black Lake in Kootenai County, Idaho 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

Black Lake is a lake in Kootenai County, Idaho covering about 0.6 sq mi, the 55th-largest of the 63 lakes SwimZone monitors in Idaho. 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, Black Lake has reached blue-green algae advisory levels in 7 of them, most recently in June 2026. This is a lake that blooms most summers. Its highest recorded reading was 2,442,660 cells/mL in June 2026.

Is it safe to swim in Black Lake right now?

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

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

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

Over 7 summers of satellite monitoring since 2020, Black Lake has reached blue-green algae advisory levels in 7 of them, most recently in June 2026. This is a lake that blooms most summers. Its highest recorded reading was 2,442,660 cells/mL in June 2026.

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

Today, 9 Idaho waters are above a safe-contact threshold and 1 more warrant caution, out of 66 monitored waters SwimZone tracks in the state.

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