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North Pond Bloom and Toxin Testing Update

Updated: Aug 14, 2020

Conditions on North Pond have improved over the past week. The most recent Secchi measurements (taken 8/12 by Debbie Cunningham, one of certified lake monitors on North Pond) was 2.2 m (7 ft). A lake is considered to be blooming if the Secchi depth is less than 2 m, so this indicates that we are experiencing some relief from the algae.

While the lake clarity had improved a few days ago, it was still a milky blue color. This color comes from cyanobacteria/blue-green algae that have died and released their pigments into the water. When the cells die, they can also release any toxins they are storing into the environment, so even though the water was clearer, it did not mean that the water was safe.

Testing for the microcystin toxin was done again today, with samples collected from North Shore Drive, the Fairview Grange, Pine Tree Camps, and Great Meadow Stream at the 225 bridge. Fortunately, all samples came back negative for the presence of microcystin! The improved Secchi and negative toxin tests suggest that the lake is currently suitable for recreating in, but users should remain vigilant and avoid any areas with surface scums.

Abraxis microcystin test results from today from samples from North Shore Drive, Fairview Grange, Pinte Tree Camp, and Great Meadow Stream. If the sample line is lighter than the control line, then there is microcystin present. All the lines here are darker than the control line, indicating no microcystin.

So does this mean conditions will stay like this for the rest of the summer?

Unfortunately, no. In the past, August and September have been the months where East Pond used to have its worst blooms. Hot calm weather can trigger stratification and further phosphorus release from the sediments, which can fuel another bloom before the summer is finished.

We will continue to do weekly toxin testing, but if conditions worsen again, we would like your help in pinpointing areas with surface scums to target testing. You can help us by reporting surface scums on your shoreline here.

What can we do to prevent another bloom this summer?

While we are at the mercy of the weather, now is the perfect time to start doing your part to reduce runoff of phosphorus into the lake. NOAA predicts this will an extremely active hurricane season, and while many hurricanes don’t last until they make it up here, the rainstorms that can accompany fizzled-out hurricanes can cause substantial runoff in the late summer and early fall. The phosphorus that runs into the lake in the next couple of months, if not used up by algae straight away, will be available to algae next summer, starting the cycle all over again. Contact the 7 Lakes Alliance for more information about how to make your property LakeSmart!

Update 8/14 - why are there so many dead fish?

Since this was posted, several people have reported seeing dead fish in the lake. Dr. Whitney King (Colby College) was out on North Pond yesterday (8/13) and took temperature and oxygen profiles:

The orange line is the dissolved oxygen (DO) in the lake. When the DO falls below 4 mg/L for extended periods of time, fish become extremely stressed and can die. Currently the bottom half of the lake is below 4 mg/L. The DO is low right now because all the dead algae in the water are decaying, which consumes oxygen in the water. Because the weather has been hot and calm, the wind isn't mixing more oxygen into the water.


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