Webster Lake in Franklin under cyanobacteria watch

New Hampshire Department of Environmental Services staff have issued a cyanobacteria watch on Webster Lake in Franklin, and cyanobacteria warnings on two other water bodies remain in effect. There aren’t any new reports on Lake Winnipesaukee.

The watch on Webster Lake was issued on Sept. 4, and remained in place as of Thursday at press time. It’s described as green ribbons of material.

Test results indicated a density of 632,000 cells per mL of dolichospermum, a form of cyanobacteria. According to the NHDES Healthy Swimming Mapper, there were seven separate reports of cyanobacteria around Webster Lake, three of which had been sampled and tested by state scientists.

Check the Healthy Swimming Mapper, which is regularly updated and describes water quality conditions throughout the state, by navigating to des.nh.gov/water/healthy-swimming/healthy-swimming-mapper.

A cyanobacteria watch is issued by NHDES staff based only on a photo, when the cyanobacteria density is approaching, but not exceeding, 70,000 cells per mL, the state benchmark; when only one sample exceeds 70,000 cells per mL; or when bloom material has passed.

Watches differ from warnings, which are issued when sample results exceed the benchmark at multiple locations. 

At Webster Lake, two locations sampled and tested by NHDES staff exceeded the benchmark, both located along its southerly shores, and another approached but did not exceed the benchmark. In four other locations, no sample was collected. 

It’s the only watch issued on Webster Lake this year, though three advisories were issued there last year. 

The only cyanobacteria warnings statewide remained in effect on Province Lake in Wakefield and Effingham, and on Tucker Pond in Salisbury. 

A cyanobacteria warning is not based on toxin evaluation, but occurs at cyanobacteria density levels when toxin production may be likely, according to NHDES staff. They’re intended to be precautionary measures for short-term exposure to toxins. When a warning is issued, resampling occurs weekly until the bloom subsides. Warnings are issued from May 15 to October 15. Watches are issued year-round, if needed. 

On Lake Winnipesaukee, there were no watches or warnings in effect on Thursday, and there weren’t any new cyanobacteria bloom reports, according to the Healthy Swimming Mapper. 

There was a new report submitted for a possible cyanobacteria bloom on Paugus Bay, though no sample had been collected. The citizen report notes the bloom was observed several weeks ago on Aug. 21 from along the shoreline, and notes surface scum and material throughout deeper waters, too. 

As the summer winds down, beaches in New Hampshire won’t be tested for the presence of fecal bacteria until next year. 

The NHDES Beach Inspection Program monitors public beaches from Memorial Day through Labor Day. NHDES staff monitor many, but not all, Granite State beaches. City of Laconia staff, for example, monitor public beaches in the city, following the same timeline as NHDES. 

Because Labor Day has passed, city staff will not sample Laconia’s public beaches until Memorial Day. Other municipalities who perform sampling themselves may maintain different policies, so it’s worth checking in with your town or city hall for accurate local information.