Is Lake Winter safe to swim?

As of July 20, 2026, Lake Winter in Sawyer County, Wisconsin is not recommended for swimming. Satellite imagery measured 608,391 cells/mL of blue-green algae on July 19, 2026, above the 100,000 cells/mL advisory threshold. Rainfall over the past week totaled 3.1 in, which can wash bacteria and nutrients into the water.

How this read is built

Lake Winter is a lake in Sawyer County, Wisconsin covering about 1 sq mi, the 155th-largest of the 337 lakes SwimZone monitors in Wisconsin. Satellite imagery measured 608,391 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, Lake Winter has reached blue-green algae advisory levels in 7 of them, most recently in July 2026. This is a lake that blooms most summers. Its highest recorded reading was 1,737,893 cells/mL in July 2023.

Is it safe to swim in Lake Winter right now?

Lake Winter is not recommended for swimming today. Satellite imagery measured 608,391 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 Lake Winter have blue-green algae (cyanobacteria)?

Yes. Satellite monitoring measured 608,391 cells/mL of blue-green algae (cyanobacteria) at Lake Winter 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 Lake Winter?

No. Blue-green algae at Lake Winter is above the safe-contact threshold (608,391 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 Lake Winter have blue-green algae blooms?

Over 7 summers of satellite monitoring since 2020, Lake Winter has reached blue-green algae advisory levels in 7 of them, most recently in July 2026. This is a lake that blooms most summers. Its highest recorded reading was 1,737,893 cells/mL in July 2023.

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

Today, 91 Wisconsin waters are above a safe-contact threshold and 11 more warrant caution, out of 564 monitored waters SwimZone tracks in the state.

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