Restoration Site:

About Issaquah Creek and Lake Sammamish State Park

Issaquah Creek drains a 61 square mile watershed to Lake Sammamish. Its headwaters are Cougar, Squak, Tiger and Taylor Mountains, while its final 6,000 feet reach runs through Lake Sammamish State Park. Unique to our local community, the Issaquah Creek watershed is over 75% forested land. Like most creeks in the area, Issaquah Creek is in a state of recovery, while facing the ongoing challenge of development. In the 1800s, the area was entirely deforested, including the along the creek, which in some locations was channelized and armored. Flatlands in the valley and near the lake shore were converted to farmland. Local hillsides were mined for coal, and until recently, coal mine tailings still contaminated the creek. (CREATE PROJECT PAGE FOR TAILINGS PILE REMEDIATION PROJECT BY CITY OF ISSAQUAH.)

Washington State Park Commission purchased the two farm parcels that comprise the park in 1951 and 1958. Lake Sammamish State Park was founded in 1953

The final stretch of Issaquah Creek — which runs through the park — is important habitat for migrating and rearing salmon. In 2005 it was identified by the Chinook Salmon Conservation Plan as a priority area for restoration efforts. Since then, Washington State Parks & Recreation Commission and the Mountains to Sound Greenway Trust have worked together to restore riparian habitat along the reach, having removed invasive flora and planted more than 50,000 native trees and shrubs along the river corridor.

2022 Restoration Project
Washington State Parks and the Mountains to Sound Greenway Trust have developed a comprehensive restoration plan to restore the entire run of Issaquah Creek within Lake Sammamish State Park. Construction takes place in the summer of 2022.

Project Goals

  1. Use historic channels and side channels to:
    1. Reconnect the creek to the floodplain and
    2. Improve fish habitat;
  2. Increase sinuosity (the natural, winding characteristic) of the creek;
  3. Incorporate large woody material in the stream to create diverse, natural conditions to benefit migrating adult salmon and rearing juveniles.

The four reaches of the project area
The restoration team has identified four unique, adjacent sections (reaches) of Issaquah Creek within the park, each with their own set of characteristics and solutions.

Reach 1: where Issaquah Creek meets the lake

In this reach, the channel is wet year-round. When flow is low, the creek slow moving and at lake level. In the past, the creek bed was channelized, and disconnected from side channels and the floodplain. This reach is appropriate for “short-term rearing habitat”. Chinook in particular linger at creek mouths during their downstream migration.

The Plan:

  • Add 35 pieces of wood throughout reach to create habitat.
  • Construct/excavate a channel to connect the existing creek to the historic creek channel (located to the northeast).
  • Add Large Woody Debris (LWD) structures at the distributary channel to “push flow” from the creek to the new channel.
  • Add two different sets of LWD to:
    1. Control sinuosity and “channel migration” (the natural tendency of a river to change course over time)
    2. Increase cover for fish
    3. Create “hydraulic complexity

Reach 2: where the river flattens out into the flood plain

This is where Issaquah Creek desposits much of its suspended sediment. The reach is mostly open with shrubby areas, invasives, and minimal forest (this forest is mostly young). This reach is appropriate for rearing juveniles and for holding areas for returning adults.

Goal for this reach: maintain the existing diverse habitat, and improve its ability to filter downstream-migrating wood debris. (Wood is important to create stream diversity and quality habitat.)

The Plan:

  • Add LWD to provide cover and hydraulic complexity.
  • Add LWD structures to filter wood traveling downstream from upper reaches.
  • Create a new channel to split the flow, directing water to a historic oxbow.
    • Add LWD and LWD structures in the new channel and the oxbow to provide cover and hydraulic diversity.

Reach 3: Narrow, high velocity flow, little habitat

Reach 3 is characterized by a channel that cuts right through, with no connection to the flood plain, with little habitat for rearing or holding, and features a potential fish barrier during high flow. The limited spawning habitat in this reach is tricky because:

  1. It is not preferred by chinook, which prefer larger gravel sizes, and
  2. While the smaller gravel sizes are appropriate for kokanee, coho and cuttroat, these fish prefer to spawn in smaller size streams.

Goals for this reach: provide hydraulic diversity to this reach to break up the flow, reconnect it to the flood plain and allow it to meander, thereby creating more habitat. 

The Plan:

  • Grade and install LWD and LWD structures to increase meandering and hydraulic complexity.
    • Initiate meandering by directing flow against stream banks — and removing roots holding banks in place in these areas.
  • Add a pedestrian bridge.

Reach 4: the uppermost reach

This reach features high hydraulic complexity and off-channel habitat. It has limited riparian forest. There is riprap armoring on one channel to prevent channel migration. It is relatively lacking in wood. While this reach is still not preferred by spawning salmon, of all the reaches, it has gravel most suitable for kokanee spawning. However, kokanee prefer smaller tributaries.

Goals for this reach: Increase hydraulic diversity and provide cover for rearing juveniles. 

The Plan:

  • Remove riprap armoring.
  • Add LWD and LWD structures:
    • seven structures to initiate large wood mass jams.
    • 14 pieces along high banks, adding hydraulic complexity and cover.
    • “apex jams” to encourage island and pool formations.
    • “spur jams” to “encourage scour of pools.”
  • Create a channel to split the flow to add hydraulic complexity.

The expected total cost of the project is $2.5 million.