• Don Yurewicz

Mystery in Dolloff Cove

On June 20th I was paddling in Dolloff Cove when I noticed a white film on the surface of the water extending approximately 10-20 ft out from the shore and along 850 ft of the lake margin.

It covered grids 624, 629, 630, 631, 635 and 636 in Zone 1 - area shaded in yellow on the map below.

Along the shore it was mixed in with a very robust accumulation of filamentous green algae floating on the surface (see photo below).


Dense mat of green filamentous algae with scattered white patches along the shore in grid 636. It is unusual to see such a dense growth of green filamentous algae this early in the summer.


Where it accumulated on the shore and examined it appeared to have a fibrous texture (see photo below).

The film largely dissipated by the next day when I collected samples for the NH DES but it was still present in some of the more protected areas along the shore. My initial assumption was that this was some sort of spill/overflow from someone's septic system in Dolloff Cove - primarily on the basis of the color of the film and its location to a specific area in Dolloff Cove. When I handed the sample off to David Neils (Chief Water Pollution Biologist for NH DES) he was puzzled - he hadn't seen something like this before. The sample was given to Kate Hastings (Cyanobacteria HAB Program Coordinator for NH DES). The bulk of the material in the water sample was green filamentous algae and pollen as I expected. There were also strands of cyanobacteria (Tolypothrix, and some Stignomea). Neither are planktonic, and are more typically seen in benthic mats or in shoreline samples. Interestingly, Tolypothrix grows as filaments and one citation states that “clumps of filaments look like wooly hair.” This would be consistent with some of the material I saw along the strand line.


So what was this white film on the lake? We are still not sure. Some possibilities include:

  • effluent from someone's septic system in Dolloff Cove.

  • bleached film of pollen or a green algae die off.

  • bleached film of a cyanobacteria bloom.

If anyone sees something unusual like this be sure to contact Maria Gross and myself (Don Yurewicz).



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