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Cyanobacteria vs Filamentous Green Algae

Quick ways to detect the differences

Download the BloomWatch app (

A cyanobacteria bloom on a NH Lake. Photo courtesy NH DES

Cyanobacteria... Cyanobacteria are photosynthetic bacteria (not algae) that produce toxins and can present a serious health risk to animals and humans when present in large numbers in a lake or other body of water. There are many types of cyanobacteria and each has their own growth requirements, produce toxins differently, and play a different role in the aquatic food web based on their size, shape and habitat. In turn, these characteristics constantly change due to wind, currents and storms.

o Formerly known as “Blue-Green Algae” — it is actually not algae but

photosynthetic bacteria. o There are thousands of species and hundreds of toxins. o They are ubiquitous in the environment and globally found. In fact, it is

understood that this bacterium has inhabited the earth for over 3.5

billion years.

Remember that Each lake is unique ... Blooms may occur anywhere on the lake! o On beaches o At boat launches o Along inaccessible shorelines o In front of private residences o As patches around the lake surface o As thick mats o Attached to rocks or substrates o Deep within the water column o Shoreline accumulations rapidly change o Weather, wind and currents may shift o Water disturbance from boats or other recreational activities can alter the

conditions of the reported bloom sighting.

One lake might have cyanobacteria and the adjoining lake won’t at all. o Sampling is not encouraged — Please avoid blooms!

o Quick fixes do not always work: Applications must be carefully considered

Expensive Continuous...even year to year Key is to report your sightings asap

Filamentous green algae ... Often called “pond scum” is characterized by intertwined long, hair-like strands, or filaments, of attached cells (often two meters in length) forming a mat that resembles wet wool. It starts growing along the bottom of shallow water or attaches to structures in the water like rocks or aquatic plants.

Filamentous green algae are naturally occurring and do not produce harmful toxins like cyanobacteria. It can, however, become a nuisance to swimmers, fishing and lake aesthetics if it becomes too abundant. It grows in response to dissolved nutrients (especially nitrogen) with increased growth and reproduction. Excessive growth of algae may indicate other pollutants have also washed into the water. (If the source of nutrients is pet or animal waste, it is likely that bacteria and other pathogens are living on the algae mats.) o It is usually seen as dull green slimy mats or clumps on the water’s

surface or hover in the water column, just beneath the surface. It is

also found along the shoreline and in shallow water. o It can appear foamy and have a bright green-yellow color, often confused

with the frequent variations of the blue-green in cyanobacteria o Mats can contain a diverse range of other organisms including

phytoplankton (sometimes a few strands of cyanobacteria), protists

and zooplankton mixed within it.


Filamentous green algae can be verified with the “stick test.” It will stick to sticks dipped into it and, if scooped into a jar, it will rest below the water’s surface.

Cyanobacteria blooms will cloud the water (in various assortment of colors.) Won’t stick to sticks and, if scooped into a jar, will always float to the top of the water’s surface.


Let NH DES coordinate sampling

Details to include in your Cyanobacteria Bloom report: o PHOTO(s) o Your Name and Contact info o Waterbody Name o Waterbody Town o Latitude and Longitude of bloom o Date, Time and Weather conditions o Description of severity and dimensions of the scum o Water conditions and other notes if possible (e.g. clarity, level and temperature

of water)

NH UNION LEADER article, dated 6/25/2020

"Beware blue-green algae in NH lakes"

Excerpts from this article:

Dr. Jennifer Graham, a limnologist with the U.S. Geological Survey, advises that if you are canoeing or kayaking and encounter a blue-green algae bloom, leave the area.

“The cyanobacteria do produce taste and odor compounds that can smell bad and so if you’re approaching an area and you can really smell an earthy or musty smell, and it’s prevalent, that’s also a good indicator that you may want to avoid the area that there may be an issue of cyanobacteria… appearing as green clouds and flecks throughout the water and along the shoreline….

She recommends notifying relevant state agencies about such sightings.

As a result of the budget freeze and the effort to maintain social distancing in the laboratory, the state isn’t monitoring water conditions at lake beaches, only ocean beaches, but still issues warnings when alerted to hazardous algae blooms.

The state has traditionally monitored water quality at beaches at lakes, great ponds, rivers as well as the ocean since 2003, relying on funding from the Beaches Environmental Assessment and Coastal Health (BEACH) Act, analyzing samples at both the state public health laboratory and the Limnology Center, both in Concord.

Testing looks at factors important to aquatic animal health such as turbidity and phosphorus, and also detects the presence of bacteria or other organisms that could be harmful to swimmers, most importantly cyanobacteria, whose growth is spurred by pollution, high temperatures and droppings from waterfowl….

Acute health effects include irritation of skin and mucous membranes, tingling numbness, nausea, vomiting, diarrhea and seizures. Chronic effects may include liver and central nervous system damage….

Dr. Amanda McQuaid of the NH state’s Harmful Algal and Cyanobacterial Bloom Program advises that people be cautious of lake water that has a surface scum and water that changes color or appears to have green streaks or blue-green flecks.

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