Mild weather leads to late-season algae blooms in lakes across King County

Blue-green algae not highly toxic, but avoid contact to be safe

Generally mild weather this fall has extended the algae-growing season on lakes across King County.

While none of the tested samples have revealed harmful levels of toxins, King County lake water quality experts recommend that people and pets avoid contact with the freshwater algae blooms. In particular, do not let dogs drink large amounts of water from lakes containing scums of algae.

Samples tested by King County Environmental Laboratory staff have identified the algae as Aphanizomenon flos-aquae, a blue-green algae species (cyanobacterium) that forms little clumps and looks like grass blades that stick together and float.

Sally Abella, a senior engineer with King County's Lakes Stewardship Program, said that concentrated amounts of the algae have been found in sheltered areas of Lake Washington, Lake Union and the Lake Washington Ship Canal, where they collect after being wind-driven across expanses of water

"This is a natural occurrence. We don't think it's especially toxic or dangerous, but to be on the safe side, we're recommending that people and pets stay away from visible concentrations of this algae," Abella said.

"When this species decomposes, it turns a bright turquoise color that some observers could confuse with paint or dye in the water," Abella said. "It actually can be a good sign when we see that color in the water, because it signals that the bloom is beginning to slow down and decay."

King County has been working with the Washington State Department of Ecology on an algae identification and testing program for lakes with frequent algae blooms. Sampling is especially important for toxic blue-green algae, which can prove fatal if ingested in large quantities.

The new DOE algae program has identified significantly toxic blooms in a number of lakes across the state this year, although none were identified in King County in 2007.

The Washington State Department of Health is developing water quality standards and uniform signage that local jurisdictions can use to warn citizens to avoid contact with the water during toxic episodes

More information about King County's Major Lakes Monitoring Program is available at http://dnr.metrokc.gov/wlr/waterres/lakes/index.htm. More information on the King County Environmental Lab is available at http://dnr.metrokc.gov/wlr/envlab/.