Is Dan Hole Pond safe to swim?

As of July 20, 2026, Dan Hole Pond in Carroll County, New Hampshire carries a swim caution. Satellite imagery measured 85,922 cells/mL of blue-green algae on July 18, 2026, elevated but below the 100,000 cells/mL advisory threshold. Rainfall over the past week totaled 0.6 in, which can wash bacteria and nutrients into the water.

How this read is built

Dan Hole Pond is a pond in Carroll County, New Hampshire covering about 0.7 sq mi, the 26th-largest of the 39 lakes SwimZone monitors in New Hampshire. Satellite imagery measured 85,922 cells/mL of blue-green algae on July 18, 2026, elevated but below 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 6 summers of satellite monitoring since 2020, Dan Hole Pond has not reached a blue-green algae advisory level. Conditions can still change quickly, so check the current read before you swim.

Is it safe to swim in Dan Hole Pond right now?

Dan Hole Pond carries a swim caution today. Satellite imagery measured 85,922 cells/mL of blue-green algae on July 18, 2026, elevated but below 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 Dan Hole Pond have blue-green algae (cyanobacteria)?

Low levels. Satellite monitoring measured 85,922 cells/mL at Dan Hole Pond on July 18, 2026, below the 100,000 cells/mL advisory threshold. Keep an eye out for surface scum, which can concentrate quickly.

Can dogs swim in Dan Hole Pond?

Use caution. Blue-green algae at Dan Hole Pond are elevated (85,922 cells/mL on July 18, 2026). Dogs are far more sensitive to cyanobacteria than people, so keep them out of the water and away from surface scum.

How often does Dan Hole Pond have blue-green algae blooms?

Over 6 summers of satellite monitoring since 2020, Dan Hole Pond has not reached a blue-green algae advisory level. Conditions can still change quickly, so check the current read before you swim.

How many New Hampshire lakes and beaches are unsafe for swimming today?

Today, 2 New Hampshire waters are above a safe-contact threshold and 1 more warrant caution, out of 61 monitored waters SwimZone tracks in the state.

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