Harmful Algal Blooms

Cyanobacteria blooms are aesthetically displeasing in sight, odor and taste, as well as potentially toxic to domestic animals, livestock, wildlife and humans.

Cyanobacteria are a potential public health danger because they may produce toxins, collectively referred to as “cyanotoxins,” that can be consumed by organisms in the food chain and released into the water when cells die. However, the amount and type of toxin produced varies over time and from lake to lake. A cyanobacterial bloom may produce very little to no toxin in one lake, and a later bloom in the same lake could produce a large toxin concentration.

Cyanotoxins can cause both acute and chronic illnesses, as these toxins target the liver, kidney and central nervous system, and can irritate the skin. Acute effects, such as skin and mucous membrane irritations, can occur after short-term exposure with water containing cyanotoxins. Chronic effects, such as liver, kidney and central nervous system damage, can occur over a long period of time from ingesting water containing toxins.

NHDES’ Harmful Algal and Cyanobacterial Bloom Program coordinates monitoring, public communication and educational outreach efforts in regard to cyanobacterial blooms.

See a Bloom?

If you suspect a waterbody is experiencing a cyanobacterial bloom, please submit a Bloom Report Form or scan the QR code at the right with your smartphone camera. Follow these steps to minimize immediate risks: 

• Don’t wade or swim or drink the water.​ 
• Keep pets or livestock out.
• Wash your hands if you’ve made contact.

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.

Drinking Water Exposure

In response to the growing concern about cyanobacteria as a threat to public health and an increase in reported bloom occurrences in New Hampshire waterbodies, NHDES now offers grants to help public water systems implement programs to monitor for potentially harmful cyanobacterial 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 source of drinking water.

Learn more about harmful algal and cyanobacterial blooms.