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Are all algae blooms toxic?

Updated: Feb 27, 2020

by Dr. Danielle Wain PhD

Danielle Wain, PhD, monitoring water quality on Messalonskee lake in September, 2019

All of the Belgrade lakes (and many lakes in Maine) have toxin-producing blue-green algae to some extent, but just because they are present does not mean that they are producing toxins.

Currently, none of the Belgrades have an algal bloom as defined by the Maine DEP (secchi depth < 2 m). But lake users should always be vigilant as wind can concentrate algae near shorelines. If the water at your beach or dock is really green, do not let pets drink the water and rinse off thoroughly after swimming. 

7 Lakes Alliance and Colby College regularly look at the types of algae present in all our lakes as part of our routine water quality monitoring.

Watershed protection is key for reducing the severity of future algal blooms and reduce the risk of toxins. Look for a more in depth discussion of cyanobacteria and toxins in the Belgrades in the upcoming Conservationist!

Here is a link to a Maine DEP fact sheet which explains more:

One of the key things to take away from the link is:

Are all Blooms Toxic? Not all blue-green algae or algal blooms are toxic.

Standard monitoring techniques cannot predict when a bloom has toxins in it. While heavy growths of blue-green algae often show detectable levels of toxins, only the most intense blooms like those above create a potential for significant toxin exposure for humans and animals.

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