Is Long Branch Lake safe to swim?

As of July 20, 2026, Long Branch Lake in Macon County, Missouri is not recommended for swimming. Satellite imagery measured 643,907 cells/mL of blue-green algae on July 19, 2026, above the 100,000 cells/mL advisory threshold. Rainfall over the past week totaled 0.0 in, which can wash bacteria and nutrients into the water.

How this read is built

Long Branch Lake is a lake in Macon County, Missouri covering about 4.3 sq mi, the 8th-largest of the 32 lakes SwimZone monitors in Missouri. Satellite imagery measured 643,907 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, Long Branch 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 1,042,949 cells/mL in August 2021.

Is it safe to swim in Long Branch Lake right now?

Long Branch Lake is not recommended for swimming today. Satellite imagery measured 643,907 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 Long Branch Lake have blue-green algae (cyanobacteria)?

Yes. Satellite monitoring measured 643,907 cells/mL of blue-green algae (cyanobacteria) at Long Branch Lake 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 Long Branch Lake?

No. Blue-green algae at Long Branch Lake is above the safe-contact threshold (643,907 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 Long Branch Lake have blue-green algae blooms?

Over 7 summers of satellite monitoring since 2020, Long Branch 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 1,042,949 cells/mL in August 2021.

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

Today, 14 Missouri waters are above a safe-contact threshold and 1 more warrant caution, out of 34 monitored waters SwimZone tracks in the state.

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