Dry conditions could cause unusually low Lake Washington lake levels

USACE/Seattle District
Published Sept. 8, 2023

 U.S. Army Corps of Engineers officials anticipate Lake Washington’s level may drop 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.

Without expected September rainfall, Lake Washington could drop below normal. There is currently only a 40 percent likelihood of this happening. Nonetheless, Corps officials expect a drop of less than 0.1 foot below normal.

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 Corps was able to fill to 21.85-feet water elevation in June this year.

Spring target levels help 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 is typical 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 advising floating homeowners, others with floating structures and vessels moored on Lakes Washington and Union and along the Ship Canal, to 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 up-to-date lake level data in the Puget Sound region, click here.

Visit www.facebook.com/ChittendenLocks or www.twitter.com/ChittendenLocks for information on activities at the Chittenden Locks.

Nicole L. Celestine

Release no. 23-027