Restoration Site:

About Lewis Creek:

Lewis Creek drains the northern slopes of Cougar Mountain into the south west corner of Lake Sammamish. The 1,000 feet of culverts under the West Lake Sammamish & I-90 interchange have divided the creek into what is referred to as the “upper basin” (not available to migrating fish, located within the city of Bellevue) and “lower Lewis Creek” (the restoration project area, located within the city of Issaquah).

Lower Lewis Creek supports kokanee, sockeye, coho and cutthroat trout.

History of changes to lower Lewis Creek
A saw mill was established on the property in 1889 near the lake shore, and a railroad ran from a pier at the lake shore, southward, to Cougar Mountain. A historic aerial photo of the area taken in 1936 indicates that: 1) the mill and railroad no longer existed by that time, and 2) the land surrounding the lake — as all land in the area — was the victim of deforestation. Remnants of the mill could still be found in the 1960s, including a large sawdust waste pile and lumber several feet thick submerged in Lake Sammamish.

In the 1980s, lower Lewis Creek experienced a large increase in residential development. The stream bed and riparian areas are owned by over 30 separate landowners. Urbanization has increased storm runoff to the creek, resulting in erosion and sedimentation of the channel, degradation of spawning habitat, and deposition of sands and fines at the mouth (the delta), which created a shallow, wide area with no deep pools for rearing. HAS THIS BEEN ADDRESSED YET? NEED PHOTOS AND RECORDS.

Goals for Restoration of lower Lewis Creek:

  • Remove any barriers within the reach.
  • Stabilize the eroding channel.
  • Create pools and other stream diversity to improve habitat for kokanee spawning.
  • Reduce fine sediment deposition within the channel.
  • Restore the mouth of the creek to provide rearing habitat for juvenile chinook.

Project Phases

2008: Removal of fish barrier

  • Location: just downstream of SE 44th Street, roughly midway between Lake Sammamish and I-90.
  • The City of Issaquah installed five rock weirs to create a series of steps to allow upstream migration past a two-foot-tall barrier

“Phase 1” (2011): Evaluate lower Lewis Creek (DID THEY WORK ON THE DELTA?)

The City of contracted Northwest Hydraulics to develop a restoration plan for the 4,125 feet of lower Lewis Creek. The plan identified four distinct “Reaches.” (See gallery.)

“Phase 2” (2015): Identify and restore the highest priority reach along lower Lewis Creek
Based on the evaluation in Phase 1, the City of Issaquah contracted Northwest Hydraulics to identify and create a restoration plan for the highest priority reach along the creek. Reach 3 was identified as having experienced channel degradation, creek bank erosion, and the loss of much of its fine bed material (gravel sizes 1/4” to 3”), and was selected to be the project area. 

Restoration work conducted on Reach 3:

  • Added Large Wood Debris (LWD) to the stream bed, spaced approximately 20-30 feet apart, to: 1) create pools, 2) promote deposits of smaller gravels, 3) make the channel more resistant to high flows.
  • Planted native riparian vegetation.

The City of Issaquah worked in partnership with the Meadowbrook Point Homeowners Association.

Potential for Future Restoration

  • “Upper reach” restoration:
    • 2,400 feet of creek, starting upstream of the 2015 lower Lewis Creek restoration project up to the culvert at I-90, have yet to be restored to:
      1. Make the channel more resistant to high flows, and
      2. Capture fine gravels suitable for spawning.
  • The Lewis Creek upper basin:
    • The major culverts under the interchange are a barrier to fish migration.
    • The ravine in this basin was characterized in 2014 as being generally steep and unstable, with the potential to provide a limited amount of spawning habitat. 
    • Due to the high cost of upgrading the culvert to a fish passage at the interchange, the upper basin was outside the scope of consideration in 2014.