Water Quality Alerts
Trouble Call Program
Foam formation on Lake Washington:
In recent weeks, many reports have been fielded by government agencies from citizens interested in the sightings of foam, observed primarily on the surface of Lake Washington. Some lakeside residents report having never seen such quantities of foam. Currently, we believe the foam formation on Lake Washington is from a natural process. Foam has been reported in many areas of Lake Washington and also on Lake Sammamish.
The physics of foam formation-how does foam form?
Foam develops when the surface tension of water molecules is reduced and the water mixes with the air, therefore producing bubbles. The reduction of water molecules can generally be attributed to surfactants such as natural organic compounds or man-made soaps and detergents. The activity of mixing is usually achieved by wave action caused by the wind. Natural surfactants can form from the biodegradation of algae (releasing algin), fish populations and other aquatic macrophytes in the water column, along with the leaching of certain types of soil. Any combination of these activities helps to produce some of the organic compounds that can contribute to the natural production of foam.
Why is the foam found in parallel lines?
The pattern of foam found on Lake Washington, and many other water bodies in King County, is due to an effect called Langmuir Circulation which is a wind induced vertical helical current in the upper layer of lakes. Langmuir Circulation is named for Irving Langmuir, who in 1938 noticed that buoyant material on the surface of water collects and concentrates in areas of a surface convergence. The foam forms bands of parallel lines, called windrows, that often occur at wind speeds between 2-7 meters/second on the surface of the lake where the convection cells converge and are dispersed by the wind. Between the streaks are areas of upwelling.
When is this event most likely to be visible?
Foam can be observed on the lake just about anytime of year, however increased reports of foam are generally made between the months of August and September. Many foam events within the lake may be related to phytoplankton populations. During one example in September 1999, a wide distribution of foam was sighted from the Bryn Mawr area near Renton, to the west channel of the I-90 Bridge. Some people thought this foam occurrence was caused by a spill, but monitoring of the lake indicated it to be a natural event. Often the foam will accumulate along the downwind shore or in coves or embayments.
Analysis of Foam Samples: Environmental scientists from the King County Environmental Laboratory have collected a number of foam samples for analysis. The samples were collected and analyzed for man-made surfactants (soaps/detergents). All of these sample results were found to be below the measurable range (<MDL), indicating commercially-made soaps were not detected. Natural foam may be brown in color, often breaks down quickly, and may have a "fishy" odor. Commercial foam is bright white, sustains its suds, and has a perfume smell.
Lake Monitoring and more information: King County routinely monitors Lake Washington, Lake Sammamish, and Lake Union. Water quality samples are collected twice each month and analyzed for specific types of bacteria, and nutrients such as ammonia, nitrates, and phosphorus, In addition, turbidity data is collected along with in-situ field measurements using a multi-parameter instrument. Field measurements include dissolved oxygen, conductivity, pH, and temperature. For more information on the water quality of Lake Washington, please visit the website:
King County Lakes
Past Action Alerts:
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