Yes, We Have Some Blue-Green Algae

Many people reported seeing lots of “little green dots” in the water this summer and sometimes they seemed to pile up in green, gunky gobs. Yes, it is a Blue-Green Algae but it also seems to be a relatively benign kind. 

The Algae, called Gloeotrichia, was found throughout the lake most of the summer in low densities. This has occurred for the past several years so it was expected this year.  However, a much denser bloom along Warren Sands the third week in August and along the south shore of the lake during the last week in August.  The increased density of the algae, the “bloom”, was probably concentrated along specific shores due to wind direction.  Samples were sent to UNH to test for toxins (this species can produce toxins at times) but this species doesn’t seem to be as dangerous as other forms of blue green algae.  There have been reports on this lake of rashes and some digestive issues after swimming which might have been due to this bloom or another cause. It is to soon to tell since we don’t have samples at the time of the reported incidents.  The bloom was largely gone by Labor Day but it is quite likely to come back next year because it has a life cycle that allows it to winter over at the bottom of the lake. More information is available in a brochure produced by the Lake Sunapee Assoc. with regard to their bloom of Gloeotrichia. The link is: Lake Sunapee Bloom. (It will download as a PDF separate from this web page.)

What individuals can do…reduce phosphorus input to lake.  The Watershed Plan is designed to do just that.   Gloeotrichia is tough to get rid of because it forms resting cells on the sediments and can draw from sediment phosphorus (accumulated from past loading) to start the cycle again. This species seems to be found in lakes that are relatively pure like Lake Wentworth, according to people from the New Hampshire Lakes Assoc., but the more phosphorus available, the worse the blooms may become.


  1. Peter (Post author)

    If the species are native, that is going to be part of the lake bottom. At the same time, more nutrient means more growth of all kinds. This goes for algae as well as plants. The nutrients come from many sources and no one person is causing this, it is the collective group. If you want your garden to grow, you fertilize it, meaning that you give it nutrients. This is what is happening to the lake and it will as long as people live around it. It will be worse if people do things like add sand to beaches that isn’t properly washed before it is added or just fertilize the lawn when it is not needed. Good fertilizer for the lawn is actually lake water, it has nutrient in it.


  2. dwr13

    Thanks for posting the information about the algae blooms. I have noticed the algae appearing during the last several years or more.
    Another concern is the amount of vegetation that is growing in the lake. I’ve been told that the vegetation is native to the lake and surroundings, but if you are like me, having come to the lake for over fifty years, you are aware that this growth has occured over the last 10 or more years. I’m wondering if others are concerned about the vegetation? It is filling in areas between Bass and Stampact islands, between Sister and Triggs and along of many shore fronts.
    D. Ross

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