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The Town of Hampstead was notified by NHDES on June 4, 2025 that the sample from the Hampstead Town Beach taken on June 3rd tested positive for Cyanobacteria and there was a visible Cyanobacteria bloom as shown in the attached image.
This is the first Cyanobacteria bloom that has ever been confirmed on Sunset Lake. Unfortunately, the number of blooms has been increasing on NH Lakes and this particular bloom is very early in the season, likely caused by all of the water runoff and nutrients getting into the lake due to the high amounts of rain this spring. Note that it is unknown how long the bloom at the beach may last, whether it will move to a different location due to wind/currents/boat waves, or if there are additional blooms in other locations. Note that there has been more filamentous green/blue algae present in other locations this year such as along the stone shorefront of Wash Pond Road, but it did not look to form a bloom. However, the recent wet/runoff conditions and current high temperatures can contribute to the formation of blooms.
If a bloom is present, the water is not suitable for wading or swimming. Exposure to the blue-green scums may cause nausea, vomiting, diarrhea, or fever in humans and pets. Anyone who comes into contact with the blue-green scum should rinse off with fresh water ASAP.
To check the current advisories for Safe Swimming please visit the NHDES Healthy Swimming Mapper: https://www.des.nh.gov/water/healthy-swimming/healthy-swimming-mapper NOTE: It appears that the Advisories/Watches/Warnings listing on the right hand side of the dashboard does not properly reflect all Advisories/Watches/Warnings (including the one on Sunset Lake), so zoom in on Sunset Lake on the map and click on the red triangle for the details.
If you think you may see a bloom, please report it using NHDES Cyanobacteria Bloom Report ASAP.
We can all do our part to reduce nutrients in Sunset Lake and help avoid Cyanobacteria blooms by following the 6 recommendations for healthy lakeshore living.
For additional information, please refer to the following links:
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