July 2019: Do’s and Don’ts of Cyanobacteria

Ahhhh, summer in New Hampshire. Millions of residents and visitors across the state enjoy our beautiful beaches, lakes and rivers throughout the season. Although the New Hampshire Department of Environmental Services (NHDES) closely monitors the quality of our lakes and ponds, you should look for cyanobacteria blooms before diving into the water. The water quality of lakes in New Hampshire is generally excellent, but it is better to be safe than sorry.

What are cyanobacteria? Cyanobacteria are naturally occurring bacteria in most of our lakes. Warm weather may promote the growth of cyanobacteria, which grow in colonies to form “blooms.” Ingesting toxic cyanobacteria may cause serious health issues for humans, pets and livestock.

Identifying cyanobacteria: A cyanobacterial bloom may appear as blue-green scums, clouds, flecks or globs. Cyanobacteria can also form green mats in the sediment and attach to rocks and other lake substrates at the shoreline. Another indicator of cyanobacteria is a green hue of the water itself. Cyanobacteria are most prevalent in the late summer months due to a combination of warm weather, rainfall, stormwater runoff and available nutrients. These conditions are favorable for the growth of cyanobacteria.  

Do’s and Don’ts of Cyanobacteria:

• DO inspect the water for bloom and scum before swimming or allowing children and pets to swim. Cyanobacteria can appear and disappear over the course of a day, so make sure to check the alerts and the water.  
• DO alert NHDES of any cyanobacteria observations at (603) 848-8094. If you can, please take a picture of the bloom or scum. NHDES will sample and post an advisory if cyanobacteria are excessive.
• DO check the NHDES website before heading for a swim at the lake. Beach advisories and cyanobacteria alerts are updated regularly on the NH Beach Advisories Map.
• DO rinse off with fresh water as soon as possible if anyone or a pet comes in contact with bloom or scum. Take the appropriate medical steps if necessary.
• DON’T swim or wade in the water if cyanobacteria are detected. Cyanobacteria are harmful to people of all ages and pets, too!
• DON’T drink the water! Direct ingestion of the bacteria may cause several symptoms, such as nausea, vomiting, fever and skin rashes and irritation. In addition, the state advises against using any lake water for consumption, since conventional in-home water treatment systems do not ensure the elimination of cyanobacteria toxins if present.
• DON’T use lake water for cooking, bathing or irrigation during bloom events. Boiling lake water with toxic cyanobacteria can potentially increase its toxicity.

For photo examples of blooms and more information about cyanobacteria, see the Cyanobacteria in New Hampshire Waters fact sheet. See our map for updates on beach advisories and cyanobacteria alerts.

This GREENWorks article can be also be found in our document library.