Is Broad Brook Reservoir safe to swim?

As of July 20, 2026, Broad Brook Reservoir in New Haven County, Connecticut is not recommended for swimming. Satellite imagery measured 643,907 cells/mL of blue-green algae on July 18, 2026, above the 100,000 cells/mL advisory threshold. Rainfall over the past week totaled 0.1 in, which can wash bacteria and nutrients into the water.

How this read is built

Broad Brook Reservoir is a reservoir in New Haven County, Connecticut. Satellite imagery measured 643,907 cells/mL of blue-green algae on July 18, 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, Broad Brook Reservoir 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 July 2022.

Is it safe to swim in Broad Brook Reservoir right now?

Broad Brook Reservoir is not recommended for swimming today. Satellite imagery measured 643,907 cells/mL of blue-green algae on July 18, 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 Broad Brook Reservoir have blue-green algae (cyanobacteria)?

Yes. Satellite monitoring measured 643,907 cells/mL of blue-green algae (cyanobacteria) at Broad Brook Reservoir on July 18, 2026, above the 100,000 cells/mL advisory level. Avoid swimming and keep children and pets out of the water.

Can dogs swim in Broad Brook Reservoir?

No. Blue-green algae at Broad Brook Reservoir is above the safe-contact threshold (643,907 cells/mL on July 18, 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 Broad Brook Reservoir have blue-green algae blooms?

Over 7 summers of satellite monitoring since 2020, Broad Brook Reservoir 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 July 2022.

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

Today, 3 Connecticut waters are above a safe-contact threshold and 27 more warrant caution, out of 92 monitored waters SwimZone tracks in the state.

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