What's that stuff in the water and is it safe to swim in?

This is the time of year where warm weather makes ideal conditions for the growth of cyanobacteria (also known as blue-green algae). As of this moment, none of the lakes except North Pond are experiencing full-lake algal blooms, but you may see some localized algae accumulation on your shoreline, depending on how the wind is blowing.


If you live on Great Pond or Long Pond, you are most likely seeing Gloeotrichia, which is a type of cyanobacteria that has adapted to low nutrient lakes by getting phosphorus from the sediments. What you see in the water are actually colonies of cells (and look like white poofballs). While Gleoetrichia is a known microcystin (an algal toxin) producer, research done on Great Pond and Long Pond indicated that Gloeo did not produce any significant amount of microcystin. A lot of Gloeo in the water may make some people itchy though. The 7 Lakes Alliance has a Gloeotrichia Monitoring Citizen Science Intiative and we get reports every week from volunteers about the density of Gloeo. The good and bad news is that it can change very quickly depending on the wind conditions, so one day your cove might have a lot, and then the next day there will be little (or vice versa!) But it is generally safe to swim in, unless you are one of the unlucky few who has a skin reaction to it.


If you live on the other lakes (particularly North Pond), the dominant type of cyanobacteria that bloom at this time of year are called Dolichospermum. This was the type of algae responsible for the 2020 North Pond bloom. Currently, the water clarity in North Pond is 6 ft at our regular deep hole monitoring site, which is considered full-lake bloom conditions. The 7 Lakes Alliance and the North Pond Association are closely monitoring the situation. We conducted microcystin testing around the lake on 8/10 (all clear!) and an experienced NPA volunteer is on hand to run tests if the conditions decline. Again, the conditions on any one camp's shoreline can change from day to day and hour to hour depending on the wind. If the water clarity drops below 3 ft at our regular monitoring site, then we do note recommend swimming anywhere in the lake. But you also should not swim in scums like the one pictured below (nor let your pets do so either!). The Maine DEP suggests that if you can't see your feet in water up to your chest, that you probably shouldn't swim in it.

Because things change so quickly, we can't come to everyone's camp and tell you if the water is safe, but it is important to note that there have been no documented cases of pet deaths due to algae in Maine, and that we have not yet detected any significant microcystin in any of the lakes (including in the middle of the North Pond bloom last year). But there is always potential for a bloom to be harmful, and some people are very skin-sensitive to the algae, so everyone needs to be aware of the conditions!


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