Mysteries of the green scum

A combination of warm temperatures, sunlight and nutrient-rich waters can cause blue-green algae to reproduce rapidly, or “bloom.”

Every so often, a green, blue-green or even red murky film will appear on the usually pristine waters of Lake Washington. What is it? Where does it come from?  Is it safe?

For many who live on or around Lake Washington, the sight of algae or green scum on the water is fleeting. But it looks suspicious. These mats or blooms of bacteria are often blown from place to place by the wind, then settle into nooks and crannies along the shore.

A combination of warm temperatures, sunlight, and nutrient-rich waters can cause blue-green algae to reproduce rapidly, or “bloom.”  Within a few days, a clear lake, pond or ditch can become cloudy with algae growth.  Blue-green blooms usually float to the surface and can be several inches thick near the shoreline.

ADVERTISEMENT
0 seconds of 0 secondsVolume 0%
Press shift question mark to access a list of keyboard shortcuts
00:00
00:00
00:00
 

In late January of this year, the King County Environmental Laboratory found concentrations above the state recreational guideline that are potentially dangerous for human health in Lake Washington. “Scums,” or accumulation of toxic algae, were found at Arrowhead Point in Kenmore, Magnuson Park and Gene Coulon Park in Renton.  The greenish water has also been spotted from time to time at Luther Burbank Park and along the Island’s south end.

Although blue-green blooms can create nuisance conditions and undesirable water quality, most are not toxic.

These floating patches consist of algae, waterborne bacteria that occur naturally in water. The patches are made up of millions of tiny living organisms that are hard to pick up or hold. They are harmless.Yet some, given just the right conditions, can turn toxic.

Toxins are created when the bacteria encounters changes in pH levels, warmer temperatures and other conditions such as nutrient loading (principally from various forms of nitrogen and phosphorus from fertilizer) and trace metals.

If the bloom is toxic, people and pets can get sick by ingesting the water or getting it on their skin, According to scientists, dogs are especially sensitive to cyanotoxins and can become seriously ill.

Engineering scientist Sally Abella of the Science and Technical Support Section of the King County Water and Land Resources Division says that the agency often finds out about such blooms from calls from individuals. Some take samples and send it to their lab.

The agency also monitors a number of buoys in Lake Washington for the presence of toxic bacteria. But there are few working working buoys on Lake Washington and elsewhere. There used to be more, Abella said.

“Many have been hit by boats or damaged over time. There is no money available to fix or replace them,” she said.

A recent report showed high toxin levels at the buoy near Coulon Beach in Renton and a buoy north of the SR-520 bridge, Arrowhead Point and on the south side of the I-90 bridge.

There are many resources that can help identify if  the algae blooms are safe. View maps of lakes and and buoy locations at https://www.nwtoxicalgae.org/FindLakes.aspx.

And let the DNR know what you have found.

“The agency welcomes input from those who spot the blooms,“ Abella said.

But when in doubt, stay out, she said; avoid all contact with water containing algae, and keep pets and animals away from the water.

 

For more, contact Abella at sally.abella@kingcounty.gov, or Doug Williams at the Department of Natural Resources and Parks at (206) 477-4543. You can also visit http://www.kingcounty.gov/environment/wlr.aspx or www.nwtoxicalgae.org.