Summer's Almost Here And Cyanobacteria Problems Back On NH Lakes And Ponds

By PAULA TRACY, InDepthNH

CONCORD, NH — June is back and so are the problems for state lakes and ponds as they relate to cyanobacteria.

Four water bodies across the southern part of the state are on the list of reported cyanobacteria blooms, as the state again begins its "response-based monitoring program" to warn the public of the potentially toxic blooms after citizens and visitors report potential problems that they see.

Pawtuckaway Lake in Nottingham, Swains Lake in Barrington, Arlington Mill Reservoir in Salem and Haunted Lake (Scobie Pond) in Francestown are all on the current state Healthy Swimmer list with reported blooms.

On May 26 blooms were reported on Swains Lake and Arlington Mill Reservoir and the others reported on May 27.

More information about cyanobacteria can be found on the state Department of Environmental Services website: https://www.des.nh.gov/water/healthy-swimming/healthy-swimming-mapper

Andrea Lamoreaux, president and policy advocate for NH LAKES said her organization, which represents most all lake associations in the state, "are concerned that conditions may be favorable for additional cyanobacteria blooms later this week. Heavy rainfall over the past several days has likely carried sediment and nutrients into many lakes, and the warm temperatures in the forecast could further promote cyanobacteria growth.

"Before entering the water, we encourage people to conduct their own risk assessment and check the Healthy Swimming Mapper to see whether cyanobacteria has been reported in the area of the lake they plan to visit."

A self-risk assessment includes looking for visible signs of cyanobacteria, such as green discoloration, surface scums, paint-like streaks, floating mats, or concentrated patches of algae. People should avoid contact with water that appears suspicious and keep pets away from affected areas, as cyanobacteria can be harmful to both people and animals.

The state cyanobacteria Harmful Algal Bloom (HABs) program uses cell density estimates taken from water bodies where the public has reported a suspected bloom to determine what type of cyanobacteria is being seen and how severe the bloom is to create its warnings.

Cyanobacteria is a naturally occurring blue-green like algae that develops on lakes and ponds and can be toxic to humans and potentially fatal to animals.

"Given the number of surface waters in New Hampshire (almost 1,000) and unpredictability of when and where cyanobacteria blooms can occur, an emphasis needs to be placed on raising awareness of those that use surface waters to recognize and avoid cyanobacteria," according to a November, 2023 state plan drafted by a 17-member advisory committee.

It said cyanobacteria have not only potential for adverse impacts to public health but also to recreation, economic interests and property values.

The state has just begun its testing season of the water on May 15. It will go through October 15, 2025 and Kate Hastings is the HABs manager for the state and above her is David Neils, chief aquatic biologist.
Cyanobacteria, according to the report https://www.des.nh.gov/sites/g/files/ehbemt341/files/documents/r-wd-23-12.pdf has been identified on 113 surface water bodies over the past five years severe enough to warrant recreational use restriction recommendations on 34 water bodies per year on average to protect public health. Bloom durations average about 25 days. Some water bodies have had a particularly hard time with recurring blooms.

The report said a goal for the state is to reduce nutrient loads such as phosphorus from entering the surface water and to innovate land use development that restricts such storm runoff from getting into the water. The report also identifies a statewide lake plan to help determine ways to protect and new laws but it concludes that cyanobacteria cannot be eliminated entirely, though new policies could be a critical line of defense.

David Neils, administrator for the Watershed Management Bureau in the water division of NH Department of Environmental Services said there have been some changes made to the state "mapper" Lamoreaux referred to.
"The Healthy Swimming Mapper (https://www.arcgis.com/apps/dashboards/8d84a6b03acb4efaab571b222c78447b) indicates the water bodies with some less severe than others," he wrote in an email Monday.

He said the "mapper" has changed slightly from 2025 for those who are familiar with it.

"We are no longer using the 'watch' category and instead have replaced that with a running list of waterbodies with confirmed reports (see “current water bodies with reported cyanobacteria blooms”). The revised option is also more user friendly as the waterbody name is “clickable” and triggers the map to zoom to the waterbody. The triangles are color coded according to the key on the bottom. We have also made 'dashboard' accessibility more prominent and the dashboard includes historic data and data/lists from the current season.

"We feel the revised system will be more transparent and less subjective. Cyanobacteria bloom 'warnings' will again be reserved for waterbodies with severe and widespread blooms," he explained.

As a reminder, he said, DES does not close waterbodies to swimming or recreation, in general. Instead the information is provided to inform the public of the conditions so they can make informed decisions about use, he said.

Starting this week, Neils said, the state will be overseeing and assisting with the fourth alum treatment in the last six years. The treatment will occur on Baboosic Lake in Merrimack and Amherst.

The permit for the treatment was issued by DES at the end of March. Baboosic Lake has experienced severe and repetitive cyanobacteria blooms for more than ten years, he said.

"The treatment will reduce the release of nutrients from the bottom sediments with a goal of reducing the internal nutrient load by 80 to 90 percent," he said.

The Baboosic Lake Association is the permit holder and prime funder of the project. Prior alum treatments have been on Nippo Lake in Barrington, Lake Kanasatka in Moultonborough, and Partridge Lake in Littleton. They all have been successful in reducing bloom frequency and severity, he said.

Lamoreaux said the legislative season which is just concluding was a productive one with several bills and conversations around finding a more continuous source of funds to address and prevent cyanobacteria blooms.

"In the end, Senate Bill 598 will create a study committee to more formally explore potential funding sources," she said. "This committee is required to submit its findings by January 1. Of the original $2 million in funding provided by the legislature and a federal source, we have about $100k remaining. House Bill 1148 from this legislative session will add cyanobacteria to discussions by the Exotic Aquatic Weeds and Species Committee. This is an ongoing committee and provides the opportunity to discuss cyanobacteria issues over time and when there is a need," she said.

This article first appeared on InDepthNH.org and is republished here under a Creative Commons license.