A pea-green scum has been observed along the shoreline of Green Lake since Sunday, Dec. 9. It was sampled by the King County Dept. of Natural Resources and found to be a blue-green algae bloom, predominantly Anabaena flos-aquae, which can produce a neurotoxin. The blue-greens float to the surface, are pushed around the lake by the wind, and then accumulate along the shoreline. The disintegrating cells can leave a pool of pigment that is a striking blue, as seen in these photos.
Blue-green algae are now called cyanobacteria, as in the following information from the Maryland Department of Natural Resources: Not all cyanobacteria blooms are toxic, and even blooms caused by known toxin producers, such as Anabaena, may not produce toxins. The toxin produced by these organisms, can poison animals if they ingest many of the cells, and the toxin may persist in the water a week or more after the bloom. The best way to minimize animal poisonings by these blooms is to keep animals away from the affected waters.