The Silver Lake Association received a couple of emails from Kate Langley Hastings, Cyanobacteria HAB Program Coordinator at the NH DES, in the last few days that there was cyanobacteria detected in Silver Lake near the boat launch in the last couple of days. The alert is based not on a tested sample but on a photograph; testing was done today (July 25) and the bloom was not detected, but visual remnants remain. The text of the messages:

From Monday:

Hi Folks,

A cyanobacteria ALERT has been issued for Silver Lake, Harrisville/Nelson. Cyanobacteria activity was first observed on 24 July, appearing asgreen ribbons of accumulated material on shorelines. See the image attached, taken today. 

This alert is based on an image, not a sample review. Sampling is scheduled for tomorrow, 25 July, I will email again with results.  

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.

From Tuesday:

Hi Everyone,

We reviewed a sample from the south end of the lake today. It appears the bloom has passed, though some remnants still persist. My coworker who sampled could see small specks in the water, you can see them by checking out the sample bottle in the picture attached. The cell count, however was low. There was 6,600 cells/mL of the cyanobacteria Dolichospermum.  The healthy swimming mapper has been updated with this information, but the alert will stay active on the map until 7/31. Cyanobacteria bloom conditions can change rapidly, so it is best to be on the watch for developing conditions.

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. NHDES will resample if worsening conditions are reported.

The photo that was reported is here.

The NH DES web site describes the cyanobacteria alert program:

The Cyanobacteria Harmful Algal Bloom Program monitors waterbodies when a potential cyanobacteria bloom is reported by a member of the public. A cyanobacteria advisory is issued lake-wide when cyanobacteria cell concentrations exceed 70,000 cells/mL. Advisories are not based on toxin evaluation but occur at cyanobacteria cell count densities when toxin production may be likely. These are intended as a precautionary measure for short-term exposure to cyanotoxins. When an advisory is issued, resampling is performed weekly until the bloom subsides. Advisories are issued from May 15 through October 15.

An alert may also be issued for a waterbody to serve as a statement to be on the watch for a potential cyanobacteria bloom. Sometimes alerts become advisories, and sometimes the bloom will pass before an advisory is issued. Alerts remain active for a week. Resampling only occurs if further bloom reports are submitted. Alerts are issued year-round as needed. An alert may be issued based upon a photo before NHDES can analyze a sample; if the cyanobacteria density is approaching 70,000 cell/mL but has not exceeded; or if the bloom has been reported to have passed by the time sample analysis is performed but may reoccur.