King County is removing invasive aquatic plants and increasing regular vegetation management to address seasonal high water levels that affect Lake Sammamish shoreline residents.

“This is a wonderful opportunity for King County to showcase its partnership with the private property owners that have seen serious degradation to their property because of rising water levels,” said King County Councilmember Jane Hague, who represents a portion of Bellevue. “We are offering a regional solution that will ensure relief and enhance recreational safety while protecting important fish habitats.”

“This proposed action plan will protect private property, address salmon habitat needs, and also meet the requirements of our maintenance agreement with the Army Corps of Engineers,” said King County Councilmember Kathy Lambert, who shares representation of the individuals that live on Lake Sammamish. “Bringing in partners such as the City of Redmond will help to ensure the success of our long-term plan for the weir and the water levels on the lake.”

The outlet from Lake Sammamish into the Sammamish River at King County’s Marymoor Park is marked by a shallow fixed concrete spillway and a wide steep section of channel downstream from the weir. This area, called the “transition zone,” is where the lake becomes the river.

Together, these features are specifically designed to pass flood flows quickly downstream, and to help hold water in the lake in summer for recreational uses, while still allowing for upstream passage of anadromous fish, including salmon returning to the Issaquah Hatchery from their time in saltwater.

The steps being taken to reduce the seasonal flooding along Lake Sammamish include:

Quadrupling the frequency of mowing in the transition zone. The dense vegetation impedes flows out of the lake. Staff will mow the area every year, and as late in the season as possible to reduce the volume of vegetation heading into the wettest time of the year;

Removing aquatic weeds in the transition zone through the King County Noxious Weed Program;

Evaluating the potential for removal of accumulated sediment in the transition zone; and

Working with the City of Redmond on a proposed project to modify the transition zone to create more capacity in the river.