Cyanobacteria Harmful Algal Blooms
Conducting monitoring, public communication and educational outreach efforts.
New Hampshire has a treasure trove of beautiful lakes, ponds and waterbodies for recreation and tourism. This webpage is dedicated to educating and communicating with the public on how to visually self-assess (use your eyes) and use the Healthy Swimming Mapper to identify if cyanobacteria blooms are present. NHDES does not close waterbodies but does recommend avoiding swimming in water in the vicinity of a bloom.
Cyanobacteria blooms are not unique to New Hampshire and are prevalent in many other states in the US and across the world. Cyanobacteria are normal, natural components of freshwater ecosystems found around the world but when water conditions are right, they can grow out of control and form surface blooms. These blooms are variously referred to as cyanobacteria harmful algal blooms, CyanoHABs or cyanobacteria blooms.
The Healthy Swimming Mapper provides warnings and watches for a static point in time (NHDES samples weekly) and blooms are dynamic (they frequently move, grow, shrink and/or dissipate). This is why a visual self-assessment when you can see the waterbody is the best tool available to stay healthy.
Cyanobacteria blooms can be harmful to pets, livestock, wildlife and people. For more information about human health effects of harmful algal blooms, visit the U.S. Environmental Protection Agency website.
Update: In 2023 and 2024, NHDES has received $1.5 million from the Governor and Legislature to help municipalities and lakes associations remediate the causes cyanobacteria blooms. This has been spent on treatment, plans and best management plans for lakes associations and New Hampshire communities.
Cyanobacteria Plan Prevention and Remediation
Report an Illness
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 and veterinarians.
Drinking Water Exposure
In response to the growing concern about the public health risks of cyanobacteria and the increase in reported bloom occurrences in New Hampshire waterbodies, 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.