Green Algae on Lake Washington Shoreline

Algae on Lake Washington Shoreline

Accumulations of the green algae Oedogonium and Spirogyra, both Chlorophyta (green) algae have been observed at Medina and Madrona swimming beaches, on Lake Washington during the last week of July. 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.

The algae at Juanita Beach was primarily diatoms, which are non-toxic and provide some of the primary productivity (plants) that are important in the food web which supports salmon and other fish in Lake Washington. At Juanita Beach there were also a small number of the cyanobacteria Microcystis sp. and Aphanizomenon sp. These species of cyanobacteria can produce toxins and are a problem when present in large numbers. The microscopic examination of the samples collected did not suggest a bloom was occurring at this time. The monitoring of these species and potential presence of toxicity are part of the routine water quality sampling carried out by King County Department of Natural Resources and Parks.

Lake Washington has it's typical good water quality this summer. The excellent water clarity may in part be responsible for the increased growth of these attached algae by allowing more sunlight lower in the water column.

Algae covering the beach and floating in the water at Madrona Beach