Dry conditions could cause unusually low Lake Washington lake-levels

Published Sept. 9, 2021

U.S. Army Corps of Engineers officials anticipate Lake Washington’s level may drop slightly below an elevation of 20 feet this month and are taking steps to conserve water during this year’s dry weather through lockage efficiency.

Current forecasts indicate the lake could drop below an elevation of 20 feet by the end of September with water levels staying low until the rain returns. Current projections suggest the lake water level could drop as low as 19.75 feet if conditions remain extremely dry for a prolonged period.

“If we don't receive typical September rainfall, Lake Washington could drop below normal,” explained Seattle District Senior Water Manager Sonja Michelsen. “There is currently only a 30 percent likelihood of this happening, and, even then, we expect a drop of less than 0.1 foot below normal. However, the worst-case dry weather condition could draw the lake down to an elevation of 19.75 feet.”

USACE typically maintains the water level between 20 and 22 feet, as measured at the Chittenden Locks. Corps officials keep winter water levels at 20 feet, and begin the annual summer refill in February, targeting a 22-foot elevation by late May to early June. The 22-feet target water elevation was accomplished in June of this year. The higher level helps meet summer water use requirements, providing water necessary for fish passage, navigation, and salinity control. Water is slowly consumed throughout the summer, until it reaches the winter level typically in early December. Since conditions have been dry this summer, Lake Washington is lower than it typically is this time of year.

The Corps is maximizing lockage efficiency by increasing the number of recreational vessels in each locking and prioritizing use of the small locks. As lake levels change, additional measures to conserve water could be implemented.

USACE officials are recommending floating homeowners, others with floating structures and vessels moored on Lakes Washington and Union and along the Ship Canal prepare for possible lower water levels.

The record low lake level is 18.35 feet, reached in 1958. The lowest recent recorded water level below 20 feet was 19.91 feet, measured in August 2015.

For more information about Locks activities visit http://bit.ly/BallardLocks or follow on Facebook, www.facebook.com/ChittendenLocks, or Twitter, www.twitter.com/ChittendenLocks.

Dallas Edwards

Release no. 21-009