By PAULA TRACY, InDepthNH.org
CONCORD – After the summer of 2024 when many lakes across the state – including Lake Winnipesaukee – had documented cyanobacteria blooms, the 2025 summer was largely the same, though there was a modification in the messaging and reporting system this year, state officials said.
However, fecal bacteria reports, particularly at ocean beaches like Hampton were up higher than the previous year with no conclusive reason, said David Neils, administrator for the Watershed Management Bureau in the Water Division of the New Hampshire Department of Environmental Services.
He said cyanobacteria blooms were documented this summer on 65 water bodies.
To research if you favorite water body had a bloom or a fecal bacteria warning, when and how long it was posted visit https://www.des.nh.gov/water/healthy-swimming/healthy-swimming-mapper
Neils said in total, the state received 515 bloom reports. There were 265 confirmed and placed on the healthy swimming mapper. The state also issued seven warnings on six waterbodies.
NHDES staff processed 500 samples in the Jody Connor Limnology Center.
Currently the swimming mapper shows a watch for Lake Kanasatka in Moultonborough which was issued on Sept. 23 and remains and one warning for Tucker Pond in Salisbury.
The state ends its monitoring for cyanobacteria every year on Oct. 15.
“The types of cyanobacteria observed in 2025 were consistent with previous years and there were no unique trends in the data. We did not receive any severe illness reports,” Neils said.
He explained DES modified its messaging and reporting system this year to be more transparent.
“The modified system included individual points on the Healthy Swimming Mapper that were color-coded to the level of cyanobacteria cell density. We reserved the issuance of ‘warnings’ in 2025 to water bodies where lake-wide blooms were occurring.
“The change was more reflective of the level of risk to humans, pets, and livestock while also stressing the importance of completing a cyanobacteria risk assessment when deciding on recreational uses,” he said.
“Overall, the cyanobacteria bloom occurrences in 2025 were about the same as in 2024 when we had 65 warnings, however, some of the warnings in 2024 were issued based on localized blooms. We feel confident that the revised public notice system used in 2025 continues to protect public health by making fully available the information we receive and samples evaluated on our Healthy Swimming Mapper. We have also provided several informational videos for public viewing discussing the risks associated with cyanobacteria, how to visually identify a bloom, and how to report a bloom.”
There are currently no fecal bacteria warnings issued by the state.
Neils said as far as our beach sampling program for fecal bacteria, the 2025 season saw more advisories on our coastal beaches than we had previously documented.
In total, there were 39 advisories issued on coastal beaches. Hampton Beach had 8 advisories (19 days, total), Jenness Beach had 3 advisories (8 days), and Wallis-Sand Beach had 1 advisory (2 days).
“There are no clear explanations for the increased number of advisories, however, we are still looking at potential sources and changes in conditions. It is unlikely we will be able to pin down any single cause and may look to do additional sampling in 2026 in order to better understand what may be going on.”
He said while the swimming season is likely over for most people “we will still be monitoring conditions and if something comes up we may issue updates as needed.”
New Hampshire has close to 1,000 lakes, ponds and water bodies for recreation and tourism.
Cyanobacteria blooms, also called “blue green algae” are not unique to New Hampshire.
While they are normal, natural components of freshwater ecosystems found when water conditions are right, they can grow out of control and form surface blooms.
Cyanobacteria blooms can be harmful to pets, livestock, wildlife and people.
In 2023 and 2024, the state Department of Environmental services received $1.5 million from the Governor and legislature to help municipalities and lakes associations with treatment, plans and best management plans.
The state website reads, “If you or someone in your family (including pets) becomes ill or develops a rash after recreating at one of New Hampshire’s surface waters, you should first consult with your doctor. You can then submit a detailed report to help us track waterborne-related illnesses. You can also check out the Center for Disease Controls fact sheets about cyanotoxin exposure for health care providers.”
In response to the growing concern about the public health risks of cyanobacteria and the reported bloom occurrences in New Hampshire water bodies, NHDES Drinking Water Bureau now offers grants to help public water systems implement programs to monitor for potentially harmful cyanobacteria blooms. Additionally, NHDES’ CyanoHAB Response Protocol for Public Water Supplies provides guidance regarding how to respond should a bloom occur within a surface waterbody used as a public drinking water source. General information about cyanotoxins in public drinking water supplies can be found through the EPA.