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Green Algae Blooms on Lake Washington Shoreline
Accumulations of the green algae Oedogonium and Spirogyra, both Chlorophyta (green) algae have been observed at swimming beaches on Lake Washington. In the past, some of these deposits were up to ten inches thick on the beach. Green algae, or Chlorophytes, do not produce toxins like some cyanobacteria (blue-green algae), such as Microcystis did in Lake Sammamish in 1997.
Microscopic photograph of the green algae Oedogonium.
Both of these green algae are very common, and grow as filaments often attached to rocks and the bottom substrate. Oedogonium has a basal cell modified into a holdfast cell. The filaments of Oedogonium are unbranched and usually rough to the touch, and parts of these filaments may break off and continue to grow. We probably see the accumulations of these algae around Seafair (mid to late July) becase the filaments have grown long enough to be broken off by wind and wave action. These accumulations are not an indication of poor water quality in the lake, although the decomposition of piles of these algae definitely degrades the immediate water quality and aesthetics, as seen in the photographs of Medina and Madrona beaches.
Microscopic photograph of the green algae Spirogyra
As these green algae decompose on the shore, they can give off a very pungent odor similar to the smell of decomposing lawn clippings. Many people have complained the odor makes them feel nauseous, produced headaches, and may have caused vomiting, but as mentioned above, do not produce toxins.
Algae covering the beach and floating in the water at Madrona Beach
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