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Cyanobacteria Water Quality Watch

Current Status: ALERT.

A cyanobacteria ALERT has been issued for Swains Lake, Barrington. Cyanobacteria activity was first observed on 18 July, appearing as subtle green mats of material growing on lake sediments in a shallow zone, occasionally with air bubbles trapped in the green material. See the images attached, taken 18 and 21 July. Samples collected and reviewed on 21 July had the benthic cyanobacteria Anabaena in dense mats. Because of the nature of benthic cyanobacteria, a typical cell count cannot be performed. Benthic cyanobacteria is different from planktonic - our more typical bloom forming cyanobacteria. Benthic cyanobacteria can still produce toxins and should be avoided, but is less likely to move around a waterbody, or affect the water beyond its presence on the bottom of the lake. Do not stir up the material and avoid swimming near it. I will check in weekly to see if the material is persisting!

NHDES urges lake users to perform visual assessments of the water prior to recreating. Stay out of the water and keep pets out if you can see any visual accumulation or coloration of the water and report it

This is not an official cyanobacteria advisory, and signs do not need to be posted. I will be in contact again if conditions change, and an official advisory is issued. 

If You Observe a Scum or Bloom:

  • Do not wade or swim in the water, especially near surface blooms.

  • Do not drink the water; avoid drawing lake water.

  • Do not let pets or livestock into or near the water; dogs are especially vulnerable to toxic cyanobacteria.

  • Report the sighting to NHDES HAB team by clicking the button above.


Fact Sheet

What is Cyanobacteria?

Cyanobacteria (formerly known as blue-green algae) are photosynthetic bacteria that utilize the sun's energy but also behave as bacteria. Cyanobacteria are some of the earliest inhabitants of our waters; naturally occur in most of our lakes, though often in relatively low numbers in New Hampshire. Many species of cyanobacteria grow in colonies to form surface water “blooms.” Blooms are usually blue-green in color and consist of thousands of individual cells. Research indicates that cyanobacteria abundance increases as lake nutrients increase, however, each taxa have their own unique requirements for growth.

About Cyanobacteria Blooms

Although most often seen when floating near the surface during the swim season, many cyanobacteria spend most of their life cycle suspended throughout the water column, regulating their buoyancy to suit their needs. Cyanobacteria can also overwinter, surviving on the lake bottom during the winter months. Increased water temperature and light in the spring promote the upward movement of cyanobacteria through the water column toward the surface where blooms or scums are often formed. The surface blooms become caught in the surface tension and are subject to dispersal or accumulation based on weather, wind, and lake morphometry. These scums are observed in summer in New Hampshire when lakes are visited the most. Though cyanobacteria blooms are sometimes reported in the fall, or even as late as when ice cover occurs.

Why is Cyanobacteria a Concern?

While cyanobacteria blooms are considered unsightly and aesthetically displeasing, there are more serious concerns associated with high concentrations of cyanobacteria. Many taxa of cyanobacteria produce toxins (cyanotoxins) and have been reported to adversely affect livestock, domestic animals, and humans globally. According to the World Health Organization (WHO), toxic cyanobacteria are found worldwide in both inland and coastal waters. The WHO has documented acute impacts to humans from cyanobacteria from the US and around the world as far back as 1890. While most human health impacts have resulted from ingestion or injection, cases of illnesses have also been attributed to swimming in cyanobacteria infested waters.

The possible effects of cyanobacteria on the “health” of New Hampshire lakes and their natural inhabitants, such as fish and other aquatic life, are under study at this time. The Center for Freshwater Biology (CFB) at the University of New Hampshire is currently examining the potential impacts of these toxins upon the lake food web and from aerosols. The potential human health hazards via exposure through drinking water and/or during recreational water activities are a concern. Exposure to toxic cyanobacteria scums may cause various symptoms, including nausea, vomiting, diarrhea, mild fever, skin rashes, eye and nose irritations, numbness, and general malaise. Some studies suggest cyanobacteria may be linked to serious illness.

Common in New Hampshire Waters?

The first reports of toxic cyanobacteria in New Hampshire occurred in the 1960s and 1970s. Cyanobacteria have been found in a majority of lakes in New Hampshire, but most often cyanobacteria numbers present in our lakes are near the minimum level of detection. The most common cyanobacteria found in New Hampshire are Dolichospermum (Anabaena), Microcystis, Aphanizomenon, Woronichinia, and Oscillatoria (Planktothrix). Though there are also unique blooms such as Gloeotrichia and Nostoc. There are several different cyanobacteria taxa found in NH waters.

Information taken directly from NH DES Fact Sheet on Cyanobacteria:

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