Cyanobacteria advisory issued on Alstead's Lake Warren

Oct. 14—ALSTEAD — The state environmental services department on Friday issued a cyanobacteria advisory for Lake Warren in Alstead, where the blue-green algae has been observed sporadically since the end of September.

But persistent cyanobacteria blooms have been seen over the past few days, "appearing as thick green clouds and swirls along some shorelines around the lake," the N.H. Department of Environmental Services said in a news release Friday afternoon.

Water samples collected Thursday show cyanobacteria concentrations as high as 2.6 million cells per milliliter. The state issues advisories when those concentrations rise above 70,000 cells per milliliter. The state continues to test samples after issuing an advisory, which is not lifted until levels drop below that standard.

The state advises people and pets to avoid water with elevated cyanobacteria levels, also known as blooms. Lake-goers should continue to monitor the shoreline of the 195-acre water body off Route 123, as blooms can change rapidly.

Cyanobacteria occur naturally in water bodies around the world, and blooms and surface scum can form due to excess nutrients, according to the release. Some cyanobacteria produce toxins that can cause a variety of acute and chronic health issues.

Photos of cyanobacteria blooms, and more information, is available at People can get updates on advisories at — BeachMaps/.

Potential cyanobacteria blooms can be reported at 603-848-8094 or

Jack Rooney can be reached at 352-1234, extension 1404, or Follow him on Twitter @RooneyReports.