Pond · Sussex County · DE
Is Big Round Pond 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 Big Round Pond right now
As of July 20, 2026, Big Round Pond in Sussex County, Delaware is clear to swim. Satellite imagery detected no blue-green algae bloom as of July 19, 2026. Rainfall over the past week totaled 0.1 in, which can wash bacteria and nutrients into the water.
Blue-green algae at Big Round Pond
Big Round Pond is a pond in Sussex County, Delaware covering about 0.7 sq mi. 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 Big Round Pond
From EPA CyAN's satellite archive
Over 7 summers of satellite monitoring since 2020, Big Round Pond has reached blue-green algae advisory levels in 2 of them, most recently in June 2022. Blooms here have been occasional rather than annual. Its highest recorded reading was 625,897 cells/mL in July 2021.
Frequently asked: swimming in Big Round Pond
- Is it safe to swim in Big Round Pond right now?
- Big Round Pond 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 Big Round Pond have blue-green algae (cyanobacteria)?
- No blue-green algae bloom is detectable at Big Round Pond 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 Big Round Pond?
- No bloom is detected at Big Round Pond 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 Big Round Pond have blue-green algae blooms?
- Over 7 summers of satellite monitoring since 2020, Big Round Pond has reached blue-green algae advisory levels in 2 of them, most recently in June 2022. Blooms here have been occasional rather than annual. Its highest recorded reading was 625,897 cells/mL in July 2021.
- How many Delaware lakes and beaches are unsafe for swimming today?
- Today, none of the 22 monitored Delaware waters SwimZone tracks are above a safe-contact threshold.
- How is Big Round 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 Big Round Pond, and a recent-rainfall overlay, all refreshed daily. It was last updated July 20, 2026.