Lake · Belknap County · NH
Is Upper Suncook Lake safe to swim?
No advisory or algae bloom reported for this water today.
Updated July 20, 2026 · EPA CyAN satellite
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What's in the water at Upper Suncook Lake right now
As of July 20, 2026, Upper Suncook Lake in Belknap County, New Hampshire is clear to swim. Satellite imagery detected no blue-green algae bloom as of July 19, 2026. Rainfall over the past week totaled 0.2 in, which can wash bacteria and nutrients into the water.
Blue-green algae at Upper Suncook Lake
Upper Suncook Lake is a lake in Belknap County, New Hampshire covering about 0.6 sq mi, the 28th-largest of the 39 lakes SwimZone monitors in New Hampshire. Satellite imagery detected no blue-green algae bloom as of July 19, 2026.
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.
Bloom history at Upper Suncook Lake
From EPA CyAN's satellite archive
Over 7 summers of satellite monitoring since 2020, Upper Suncook Lake has not reached a blue-green algae advisory level. Conditions can still change quickly, so check the current read before you swim.
Frequently asked: swimming in Upper Suncook Lake
- Is it safe to swim in Upper Suncook Lake right now?
- Upper Suncook Lake is clear to swim today. Satellite imagery detected no blue-green algae bloom as of July 19, 2026. Conditions can change quickly with wind, heat, and rain, so check the posted signs and look at the water before you get in.
- Does Upper Suncook Lake have blue-green algae (cyanobacteria)?
- No blue-green algae bloom is detectable at Upper Suncook Lake as of July 19, 2026 (below the satellite's roughly 10,000 cells/mL detection limit). Cyanobacteria can still appear within hours in warm, calm, nutrient-rich water, so look before you swim.
- Can dogs swim in Upper Suncook Lake?
- No bloom is detected at Upper Suncook Lake today, but dogs are much more vulnerable to blue-green algae than people, and blooms can form within hours. Always keep dogs away from water that looks green, scummy, or discolored, and rinse them off after swimming.
- How often does Upper Suncook Lake have blue-green algae blooms?
- Over 7 summers of satellite monitoring since 2020, Upper Suncook Lake 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 Upper Suncook 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 Upper Suncook Lake, and a recent-rainfall overlay, all refreshed daily. It was last updated July 20, 2026.