Corps of Engineers begins Lake Washington annual summer refill

Published Feb. 14, 2020

SEATTLE – U.S. Army Corps of Engineers officials have been working to help clear the highest inflow event at the locks since detailed record keeping began, but will start Lake Washington’s annual summer refill operations February 15, 2020.

Between February 7-9 the peak inflow was between 15,000 and 16,000 cubic feet per second (cfs). The average inflow over this period was 13,700 cfs. Typical inflow to the lake in early February is about 2,000 cfs. Water managers were releasing about 13,500 cfs from the spillway, which is the maximum spill capacity for the current lake level.

“Detailed record keeping began in 1946,” said Seattle District Hydrology Section Chief Ken Brettmann. “Essentially, this is the largest inflow event since World War II.”

There were similar big events in February 1996 and January 2009, but according to Brettmann, the event this February appears to be the largest in the database.

During the refill vessel owners should closely monitor lake elevations and adjust mooring lines as necessary.

Water managers are targeting a typical annual refill of the lake to elevation 22 feet this spring. Fill rates and target elevations vary through May based on conditions. Refilling the lake to 22 feet will help meet increased summer water use, providing water necessary for fish passage, navigation and salinity control.

Private and commercial maritime interests along Lake Washington Ship Canal and in Lakes Washington and Union should expect a gradual rise from the winter level of 20 feet until the 22-foot target refill elevation is reached around June 1.

The official lake level is measured at the Locks. The 22-foot target elevation is referenced to the local project datum, equivalent to 18.75 feet referenced to the North American Vertical Datum of 1988. Lake Washington and Lake Union levels may vary due to natural gradient between the lake and the locks, or wind that can push the lake levels up for short durations. Depending on conditions, the lake may remain at the maximum target elevation through June and July.

More information on Lake Washington’s status is available on the Corps’ Seattle District Reservoir Control Center website at

For more information about activities at the Locks, visit the Locks’ Web site at Also follow the Locks on Facebook and Twitter,

Bill Dowell

Release no. 20-010