HOLLIS — New Hampshire Department of Environmental Services officials issued a cyanobacteria warning for Silver Lake in Hollis after observing a bloom this week.

Samples collected from the boat launch exceeded the state threshold of 70,000 cells per milliliter of cyanobacteria. Cell concentrations from the boat launch were 971,000 cells per milliliter.

This is the second advisory issued for the lake this summer. The first advisory was issued in June and weekly samples from the lake have been collected since then. Samples collected on Tuesday contained a mix of cyanobacteria taxa.

As a result, DES officials issued a cyanobacteria advisory for those who swim at the beach and use the waterbody for recreation. It is also advised to look out for accumulations in other areas of the lake and avoid contact. Please continue to monitor your individual shoreline for changing conditions.

The advisory will remain in effect until NHDES confirms that cell concentrations of the bloom have subsided.

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.

The department advises the public to 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.

Newsletter