What are cyanobacteria?

Cyanobacteria are actually a group of bacteria that are closely related to algae; however they are not considered algae. They are the only group of bacteria that photosynthesize, or use light and carbon dioxide to create their own food the same way that plants do. Different types of cyanobacteria may be green, blue, red, or brown, but the one thing they have in common is their tendency to float on the surface in a layer that is often described as “oily” or “scummy” looking.

What is a cyanobacteria bloom?

A “bloom” is a generic term used for rapidly reproducing colonies of bacteria or algae in bodies of water. These blooms tend to occur in bodies of water that have received a high input of nutrients, either by being disturbed from a sediment bed where it previously laid dormant, or from some external input of nutrients, such as from fertilizer runoff.

Why are cyanobacteria blooms “bad”?

While cyanobacteria itself are not a “bad” or harmful organism, and live naturally in almost every type of environment on our planet, blooms of certain cyanobacteria can have negative impacts in two major ways:

  1. Some species of cyanobacteria release toxins which, when present in high concentrations, can be harmful to humans, pets, fish, and other aquatic organisms.
  2. When colonies of bacteria or algae bloom, they quickly consume all available nutrients in an area and then tend to die quickly; when they die, the blooms are consumed by other bacteria that use up oxygen, this in turn can create a low-to-no oxygen or “anoxic” zone in the water that fish and other organisms that need oxygen cannot tolerate.

Does climate change impact cyanobacteria blooms at all?

Warmer temperatures, such as those caused by global warming/climate change, can increase both the frequency and intensity of cyanobacteria blooms. This is due to the fact that these bacteria prefer warmer temperatures, and so a longer, warmer summer season provides more opportunity for blooms. Water stratification (lack of mixing in the water column) is also increased when waters warm more, allowing bacteria to remain thriving at the surface of the lake with plenty of sunlight available.

Read more about how climate change and global warming can increase cyanobacteria blooms here:

What we’re looking for: Cyanobacteria

**It is important to note that blooms of this size are entirely unprecedented on Squam, below is an example.









Cyanobacteria bloom in Bow Lake, Northwood, NH. Photo - NHDES


Don’t be mistaken by look-alikes

Imposter: green algae

Algae blooms will often have a similar green color and dispersal pattern to cyanobacteria blooms- one way to distinguish is that algae blooms will typically be less of a film on the water and more of a thick mat. Cyanobacteria tends to almost look like paint that has been spilled, and can also be other colors besides green such as red, blue, and brown. Green algae can be see floating in stringy blobs that look like tumbleweed floating through the water or settled on the lake bed. However, there are several exceptions to both of these generalities and if you are unsure whether something is algae or cyanobacteria, feel free to snap a picture and submit it in the reporting form on the SLA website (see below).





Green algae blooms. Photo - Ohio EPA









Imposter: Pollen

Pollen may aggregate in lakes due to winds, but typically will have a paler or more yellow color than cyanobacteria.









Pine pollen. Photo - LSPA

If you are unsure whether something in the lake is cyanobacteria, snap a picture and upload it with the SLA reporting form here:


What is the Squam Lakes Association doing about cyanobacteria?

The SLA is developing a monitoring plan. This also means we will be looking for volunteers to help with monitoring, and if you have any interest whatsoever in contributing your time please let us know.

In addition to this plan, the SLA is currently leveraging our updated the 2019 Squam Lakes Watershed Plan to reduce activities that can increase cyanobacteria blooms, found here:


What can I do about cyanobacteria blooms?

The best thing residents and visitors of the Squam region can do to combat cyanobacteria blooms is to help prevent them. The primary cause of cyanobacteria blooms is excess nutrients, and the following can be done to reduce and prevent accidental nutrient pollution of water sources:

  • Minimize the use of fertilizers in yards and gardens, and follow guidelines to maximize absorption so as little as possible escapes as runoff
  • Make sure your household septic system is always properly maintained to reduce leaks and water contamination
  • Allow natural plants to remain around shores of the lake to act as a natural buffer for incoming water runoff

For even more tips on how to reduce water pollution, and other ways to care for Squam Lake, check out the “50 Ways to Care for Squam” on our website ​


What if I suspect a bloom is occurring?

Please call NHDES immediately at (603) 848-8094 (Beaches/Cyanobacteria Hotline), or (603) 271-0698 (office of Amanda McQuaid), or and they will conduct a site visit. You may also collect a sample in a clean container (plastic or glass jar) and bring it to NHDES in Concord to identify.

Caution: If collecting a potentially toxic algal sample, avoid contact with skin. Wear water-proof gloves when sampling and/or immediately wash all areas of the body where water contact has occurred.

 * The SLA can provide assistance in any part of this process! *

General info: (603) 968-7336    or
Tyson Morrill, SLA's Director of Conservation at


Which beaches are closed ('advisories')?

Advisories can put users on notice or close beaches all together due to concerns like E. coli, cyanobacteria or contamination. These events are seasonal and are frequently influenced by weather conditions. 
Click here for the updated list of beach advisories


History of cyanobacteria in the Squam Lakes Watershed

In September 2017, a sample from Squam contained at least two types of the bacteria- Anabaena and Aphanocapsa. It was a small, isolated event that did not cause any known incidents or issues for those on the lake. The small bloom from 2017 is pictured below. In October 2018, a cyanobacteria bloom was reported on White Oak Pond. The bloom cleared within several days.