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Environmental Data in King County, Washington

Trouble Call Program

Water Quality Alert:

Lake Washington Water Clarity

In the last week, there have been a number of water quality alerts from citizens at the north end of Lake Washington. On Tuesday, March 8th 2005, the King County Environmental Lab received a report of a 1 mile long "oil slick" located offshore of Matthews Beach. We dispatched a field crew and vessel. Environmental scientists observed a brownish-green material on the lake surface. Water quality samples were collected and the area was photographed.

Water samples were analyzed for phytoplankton analysis by the lab's microbiology unit. Four samples were collected within the proximity of the greenish-brown material.

Upon microscopic examination of the floating portions of samples, we found the same dominant algae, Botryococcus sp.. Botryococcus sp. is a green algae which forms a free-floating colony of indefinite shape within a tough sheath. Under the right conditions, generally in the fall, this alga may contain large amounts of oil in its cell body. Although this is not the season where large amounts of oil are accumulating in the cell, there is likely to be some oil production accounting for the appearance of a sheen on the water and the persistent floating property. The floating brown and greenish-brown material were quite likely mats of Botryococcus sp.. The dominant alga in a different sample was Aphanizomenon sp., a cyanobacteria or bluegreen filamentous alga. The dominant alga in another sample was Chlamydomonas sp., a green, motile alga. Both of these samples also contained Botryococcus sp..

In addition to the algal activity on Lake Washington, the lake level is rising thereby floating large amounts of partially decomposed vegetation off the shoreline. This vegetative material gives the water a brownish hue. The US Army Corps of Engineers is raising the water level of Lake Washington to its spring level. The Corps regulates the lake level through its operations at the Hiram M. Chittenden Locks in Ballard. A map with corresponding hydrographs of the lake level are available HERE.

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