The New Hampshire Department of Environmental Services has confirmed the presence of toxin-producing species of cyanobacteria in the waters of Pleasant Lake in New London off the beach at Slope 'n Shore. The concentration is 161,800 cells/ml, which is much higher than the 70,000 cells/ml considered by the state to be potentially dangerous.
This bloom is near the outlet of the skating pond at the corner of Pleasant St and Knollwood Rd, in the Slope ‘n Shore development. You can get more information about this bloom, including photos, from the NH DES Healthy Swimming Mapper here. For more information about cyanobacteria blooms, consult the PLPA website here, or the NH DES CyanoHAB website here.
Since there is currently no signal of this bloom from the PLPA cyanobacteria sampling buoy near the center end of the lake at the Elkins end, this bloom is likely a localized event. We do not know if there are other localized blooms around the lake, but hot days create conditions that favor blooms. So it is important to be vigilant.
Keep a close eye out for discolored or cloudy water and avoid water contact in these areas. Note that toxins can be present even in waters that appear clear, and it is particularly important to keep pets and small children out of the water, as they are much more susceptible to the harmful and potentially fatal effects of the toxins.
We will follow up as more information is received.
Below is the report received from NHDES:
A cyanobacteria bloom has been observed at your lake, please see below for details.
Waterbody | Pleasant Lake, New London |
Status | REPORT |
Issued | 6/30/2026 |
Bloom Description (photos attached) | Shoreline accumulation of bloom material near Slope ‘n Shore Beach at northwest end of lake near inlet, observed from shore only |
Cyanobacteria Taxa | Dolichospermum lemmermanii |
Cyanobacteria Density (cells/mL) | 161,800 cells/mL |
Notes | Bloom reported by local resident based on shoreline observation, sample submitted for evaluation. Please report through the Bloom Report Form if you continue to see bloom conditions. |
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Please visit the Healthy Swimming Mapper for the most current information about bloom location, status, and severity.
Cyanobacteria reports depict only what an observer sees in the water. The report may reflect a waterbody wide perspective if they boated around the waterbody and made observations, or it could be a single sighting from the shoreline. One sighting does not indicate that a warning is necessary, but it does indicate that those on or around the waterbody should be aware that cyanobacteria have been observed beyond what is natural, and that they should be on the lookout for shifting bloom conditions and report them via the Bloom Report Form. Reports will be removed from the Healthy Swimming Mapper after one week if no further reports are received.
Warnings are issued when samples are evaluated microscopically, and cell counts exceed 70,000 cells/mL and the bloom is widespread or extends to multiple locations on the waterbody. A warning does not close the waterbody to recreational use. The warning is intended as a precautionary measure to inform the public of the potential health risks associated with cyanobacteria blooms. Please see our FAQs for more information.
NHDES advises lake users to not swim in or near the vicinity of where bloom material is visible. Please also keep pets and livestock out of areas where bloom material is observed. It is suggested that local authorities post an informational cyanobacteria sign at public access points.
Please forward this email to other residents / community members who may benefit from this information. If they would like to be added to the email distribution list, please have them sign up to be directly included on future communications from NHDES. If you prefer to no longer receive these sampling updates, simply respond, and indicate "unsubscribe".
Best,
The CyanoHAB Team
Cyanobacteria Harmful Algal Bloom Program
Watershed Management Bureau, Water Division
New Hampshire Department of Environmental Services
29 Hazen Drive, P.O. Box 95, Concord, NH 03302-0095
603-848-8094 hab@des.nh.gov
Report a Bloom
Healthy Swimming Mapper
