Working for a safe, affordable, vibrant, innovative, and interconnected city.
Learn More
Seattle.gov Home Page
Seattle.gov This Department

Current Water Supply Conditions and Outlook

  • Masonry Pool. This photo was taken April 19, 2015 by Josephine West.

April 21, 2015

Supply Outlook

Our current water supply and outlook is good despite the low snowpack in the Cedar and South Fork Tolt watersheds.

Last week, 0.91 inches and 1.53 inches of precipitation were recorded in our Cedar and South Fork Tolt River watersheds respectively, some of which fell as April snow at the higher elevations! However, with unseasonably warm temperatures and precipitation falling as rain through much of the winter season, snowpack in our mountain watersheds is well below the long term average for this time of the year. In order to meet our normal goal of refilling our reservoirs toward the end of the spring, we are relying more than usual on rainfall than snowmelt. As part of this strategy, we maintained our reservoir water levels somewhat higher than normal in the winter while meeting multiple objectives (i.e., municipal water supply, flood management, hydropower and protecting salmon redds).

We have transitioned into the spring reservoir refill period with both the Chester Morse Reservoir and the South Fork Tolt Reservoir in the upper range of their target elevations for refill. Moving forward, we will manage the reservoir water levels in the upper range for refill.

Chester Morse Lake at the Overflow Dike is at elevation 1563.8 feet, about 0.2 feet higher than last week, and about 8.4 feet above its long term average (based on the years 1989 to 2005). Masonry Pool Reservoir at Masonry Dam is at elevation 1563.7 feet, about 0.1 feet higher than last week, and about 9.6 feet above its long term average. The South Fork Tolt Reservoir at the South Fork Tolt Dam is at elevation 1762.8 feet, about 0.2 feet lower than last week, and about 2.3 feet above its long term average. Water releases from reservoir storage are actively being managed for water supply, fish habitat, hydropower and flood management objectives for both the Cedar and South Fork Tolt Rivers.

Water consumption for the previous seven days averaged approximately 107 mgd. That is more than the 103 mgd consumed during the same period last year, and less than the average of 116 mgd used during the same period over the years 1999-2008.

Juvenile sockeye salmon are emerging from their redds (spawning nests in the gravel of streams) and migrating to Lake Washington on a nightly basis. Juvenile Chinook salmon have begun to emerge from their redds to migrate to the river margins to rear, although many will also move to Lake Washington for rearing. Redd surveys in the Cedar River below Landsburg have identified one steelhead redd and 6 trout redds. Young coho, steelhead and trout that emerged in 2014, are rearing in the Cedar at this time.

Tolt summer-run steelhead move into the upper reaches of the South Fork Tolt River during the summer and fall where they wait to spawn during the following winter and spring. At this time, early spawning steelhead in the population have begun to construct redds. These early redds will start to produce emerging fry in late April. Adult summer steelhead will continue to spawn into the month of April. Young steelhead and coho that emerged in 2014 are currently rearing in the South Fork Tolt. Juvenile Chinook salmon in the mainstem Tolt River have begun to emerge from their redds and will be rearing in the mainstem into the month of July.

View Current Water Supply Graphs (pdf)

Related links

Landsburg Mitigation
Water Sources and Treatment