State Issues Cyanobacteria Advisories and Alerts in New Hampshire

Concord, NH- Several cyanobacterial blooms have been observed in New Hampshire this month. “Cyanobacteria Advisories” are issued when samples are collected and identified with cell concentrations exceeding the state threshold of 70,000 cells/ml. “Cyanobacteria Alerts” are shared when photos and reports have been submitted to NHDES (and no samples have been collected or if blooms have already dissipated). Advisories and Alerts are not based on toxin evaluations and are intended as a precautionary measure. These messages are shared to inform the public to be on the lookout, and to be cautious in waterbodies with blooms.

Four advisories have been issued:

• Governors Lake, Raymond (May 27 – June 10)

• Clough Pond, Loudon (June 2 –June 10)

• Millville Lake, Salem (June 3- June 10)

• Silver Lake, Hollis (June 8- current)

There have also been several other bloom sightings, and alerts have been shared amongst the communities. These blooms have been reported, but either dissipated quickly, or did not have concentrations exceeding 70,000 cells/ml. Blooms have also been mixed with pollen and appear in a variety of colors.

Blooms observed:

• Lake Winnepocket, Webster

• Island Pond, Stoddard

• Mascoma Lake, Enfield

• Phillips Pond, Sandown

• Locke Lake, Barnstead

Learn more about Harmful Cyanobacterial Blooms and Advisories in New Hampshire:

Cyanobacteria Facts

Is that cyanobacteria? Maybe it is green filamentous algae?

NH Cyanobacteria and Beach Bacteria Advisories

Cyanobacteria Press Releases

Blooms may appear blue-green, but also display a variety of colors as it grows and decays, or when mixed with other debris such as pollen or other phytoplankton. These organisms are suspended throughout the water column, but often get caught at the surface or shorelines during rapid growth. The blooms typically move around the lake which is sometimes driven by lake currents and prevailing winds. The conditions may rapidly change at your individual shorelines. As the bloom dies, you may also see white clouds near shorelines of the lake. Be cautious of lake water that has a surface scum, changes colors, or appears to have green streaks or blue-green flecks aggregating along the shore. 

Cyanobacteria are natural components of water bodies worldwide, though blooms and surface scums may form when excess nutrients are available to the water.  Some cyanobacteria produce toxins that are stored within the cells and released upon cell death. Toxins can cause both acute and chronic health effects that range in severity.  Acute health effects include irritation of skin and mucous membranes, tingling, numbness, nausea, vomiting, seizures and diarrhea. Chronic effects may include liver and central nervous system damage.