Is Old Oyster Bayou Lake safe to swim?

As of July 20, 2026, Old Oyster Bayou Lake in Terrebonne County, Louisiana is not recommended for swimming. Satellite imagery measured 1,013,778 cells/mL of blue-green algae on July 19, 2026, above the 100,000 cells/mL advisory threshold. Rainfall over the past week totaled 4.5 in, which can wash bacteria and nutrients into the water.

How this read is built

Old Oyster Bayou Lake is a lake in Terrebonne County, Louisiana covering about 0.5 sq mi, the 176th-largest of the 215 lakes SwimZone monitors in Louisiana. Satellite imagery measured 1,013,778 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, Old Oyster Bayou Lake has reached blue-green algae advisory levels in 4 of them, most recently in July 2024. Its highest recorded reading was 608,391 cells/mL in July 2024.

Is it safe to swim in Old Oyster Bayou Lake right now?

Old Oyster Bayou Lake is not recommended for swimming today. Satellite imagery measured 1,013,778 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 Old Oyster Bayou Lake have blue-green algae (cyanobacteria)?

Yes. Satellite monitoring measured 1,013,778 cells/mL of blue-green algae (cyanobacteria) at Old Oyster Bayou 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 Old Oyster Bayou Lake?

No. Blue-green algae at Old Oyster Bayou Lake is above the safe-contact threshold (1,013,778 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 Old Oyster Bayou Lake have blue-green algae blooms?

Over 7 summers of satellite monitoring since 2020, Old Oyster Bayou Lake has reached blue-green algae advisory levels in 4 of them, most recently in July 2024. Its highest recorded reading was 608,391 cells/mL in July 2024.

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

Today, 69 Louisiana waters are above a safe-contact threshold and 36 more warrant caution, out of 265 monitored waters SwimZone tracks in the state.

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