Lakes in Jaffrey and Rindge under cyanobacteria alerts

  • Contoocook Lake is one of two local lakes, along with Lake Monomonac, under a cyanobacteria alert after algae blooms were spotted at the end of August. STAFF PHOTO BY ASHLEY SAARI—

Monadnock Ledger-Transcript
Published: 9/5/2023 12:23:08 PM

Cyanobacteria alerts for Lake Monomonac in Rindge and Contoocook Lake in Jaffrey and Rindge are active through this week, after sightings of blooms in both lakes at the end of August.

Cyanobacteria, or blue-green algae, are a toxic algae bloom that can cause illness in animals and people. Symptoms can vary based on how a person was exposed, for how long and which type of cyanotoxins were ingested. Effects can be caused by skin contact, breathing in water droplets, ingesting contaminated water or eating fish or shellfish containing the toxins. Symptoms include irritation of the skin, eyes, nose, throat or lungs, which can be caused by contact. For those who eat contaminated food or swallow contaminated water, symptoms can include stomach pain, headache, muscle weakness, dizziness, vomiting, diarrhea and liver damage.

A cyanobacteria bloom was seen in Contoocook Lake, which straddles the Jaffrey and Rindge border, on Aug. 29, with reports of green streaks and accumulations on the water’s surface. The bloom was not visible as of Aug. 31, but bloom conditions can fluctuate rapidly based on the amount of nutrients in the water. There was not a sample taken, and there is not information available about possible cyanobacteria levels, but an alert has been issued based on the sighting.

While not an official cyanobacteria advisory, the New Hampshire Department of Environmental Services is urging lake-goers to visually check for cyanobacteria blooms prior to using the water. If there is any visual accumulation of algae or discoloration of the water, people should stay out of the water and keep pets from drinking or swimming. If bloom conditions reoccur, and are reported, sampling will be scheduled to monitor cyanobacteria levels.

At Lake Monomonac, cyanobacteria was observed on Aug. 21, with reported algae blooms spotted as green clouds in the water and specks on the water’s surface. Water samples were collected on Aug. 24, which contained counts of cyanobacteria, specifically dolichospermum and woronichinia, in concentrations up to 13,798 cells/mL in areas of highest observed accumulations. While this is well below the advisory level for cyanobacteria – which is 70,000 cells/mL – the bloom appears to be widespread, which could develop into a more-significant contamination.

The New Hampshire Department of Environmental Services will resample if worsening conditions are reported. 

Ashley Saari can be reached at 603-924-7172, Ext. 244 or She’s on Twitter @AshleySaariMLT.

Sign up for Monadnock Ledger-Transcript Newsletters
Monadnock Ledger-Transcript Headline Alerts
Monadnock Ledger-Transcript MLT Minute North
Monadnock Ledger-Transcript MLT Minute South
Monadnock Ledger-Transcript Real Estate & Transactions
Monadnock Ledger-Transcript Contests and Promotions
Monadnock Ledger-Transcript Dining & Entertainment
Monadnock Ledger-Transcript Sports


Support Local Journalism

Subscribe to the Monadnock Ledger-Transcript, your source for Peterborough area news.

Monadnock Ledger-Transcript

20 Grove St.
Peterborough, NH 03458


© 2021 Monadnock Ledger-Transcript
Terms & Conditions - Privacy Policy