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Mitigation sites

Mitigation Sites

Mitigation Reserves Program

The King County Mitigation Reserves Program In-Lieu Fee Mitigation Program is a state- and federally- authorized In-Lieu Fee Mitigation Program that provides an option for permittees with unavoidable impacts to wetlands and aquatic resources to pay a fee to King County instead of completing their own offset project. Fees collected are used to design and construct mitigation projects that restore wetlands and aquatic resources to offset the mitigation obligations. 

Boise Creek Mitigation Project

The Boise Creek Mitigation Project is located on a 4.5-acre portion of the Middle Boise Creek Natural Area on the left bank of Boise Creek downstream from 284th Ave SE. The Boise Creek Mitigation Project will create wetland and aquatic habitat while preserving native riparian buffers. Construction begins in 2024 and the completed project will create 2 acres of new wetland and aquatic area. The Boise Creek Mitigation Project will compensate for unavoidable permitted impacts to wetlands and aquatic resources in Water Resource Inventory Area (WRIA) 10.

For more information, see the Boise Creek Mitigation Project page.


Rainbow Bend Mitigation Project

The Rainbow Bend Mitigation Project is located on a 19.78-acre portion of the Larry Phillips Natural Area at river mile 11.5 on the right (northeast) bank of the Cedar River, a short distance downstream of the Cedar Grove Road bridge. The Rainbow Bend Mitigation Project will re-establish and enhance wetland and aquatic habitat; preserve large trees; add floodplain roughness and fish and wildlife habitat through the installation of large wood and snags; and restore natural functions and processes to the Cedar River floodplain. This project adds to the successful Rainbow Bend Levee Removal and Floodplain Reconnection Project that was constructed in 2013. Construction begins in 2023 and the completed project will create 6.4 acres of new, primarily forested, wetland while preserving large trees and enhancing existing upland areas. It will also create new floodplain channels and enhance existing channels. The Rainbow Bend Mitigation Project will compensate for unavoidable permitted impacts to wetlands and aquatic resources in the Cedar River/Lake Washington Service Area.

For more information, see the Rainbow Bend Mitigation Project page.


Chinook Wind Mitigation Project

Construction completed 2022

The Chinook Wind Mitigation Project site was acquired in September 2015. The 5.912-acre project is located on the Duwamish River in the Green/Duwamish River Watershed (WRIA 9). With its location in the transition zone of the Duwamish River, the Chinook Wind Mitigation Project will provide much needed habitats in this key reach of the river. These include sheltered off-channel habitat surrounded by mudflat, low marsh, high marsh, and riparian habitats.

The Duwamish Estuary is vitally important to the region, both as an integral ecological link between the Green River and Puget Sound and as a center of trade and commerce that supports local jobs and strengthens Washington’s economy. But, decades of heavy industrial use in the Duwamish corridor has taken its toll. The WRIA 9 Salmon Habitat Plan notes that, “the Duwamish has lost 97% of the habitat it provided 150 years ago. The Duwamish also suffers from decades of industrial pollution that have resulted in the lower five miles of the river becoming a Superfund cleanup site. Scientific assessment work for th(e) Plan suggests that this loss, degradation, and fragmentation of estuarine habitat in the Duwamish – particularly transition zone habitat — is a limiting habitat factor for the Chinook populations of the (Green-Duwamish) watershed”.

For more information, see the Chinook Wind Mitigation Project page.


Taylor Creek Mitigation Project (Cedar River)

Construction completed 2019

The Taylor Creek Mitigation Project will restore stream and wetland habitat within the lower reaches of Taylor Creek. The project demolished all buildings, regraded stream and floodplain areas to emulate historic conditions, and installed large wood and native plants throughout the property. These actions resulted in about 13 acres of habitat improvement. The project connects two previous King County restoration sites and will result in a 27-acre riparian corridor with high quality fish and wildlife habitat.

For more information, see the Taylor Creek (Cedar River) Mitigation Project page. 


Issaquah Creek Mitigation Project

Construction completed 2019

Located in the Sammamish River Watershed, the Middle Issaquah Creek Natural Area consists of 41.3 acres of public land along Issaquah Creek. Located within the Middle Issaquah Creek Natural Area, the Issaquah Creek mitigation project will remove existing fill, create wetlands, place large wood and wildlife trees, and restore native vegetation to create a riverine wetland that improves water quality and hydrology, and provides habitat for fish and wildlife.

For more information, see the Issaquah Creek Mitigation Project page.


Taylor Creek Headwaters Wetland Preservation Project

The 12.19-acre Taylor Creek Headwaters Wetland Preservation Project, located in the Cedar River / Lake Washington Service Area, was acquired by King County to preserve the wetland and its buffer. Phase I of this project was acquired in 2015 (11 acres) and Phase II was acquired in 2021 (1.19 acres). King County’s Mitigation Reserve Program will earn in-lieu fee mitigation credits through the preservation and stewardship of 4.14 acres of intact Category I wetland and 8.05 acres of surrounding upland in the Skyway area of unincorporated King County. 

Taylor Creek Headwaters Wetland is a depressional flow-through wetland with a sizable buffer of mature mixed coniferous forest that is situated at the headwaters of Taylor Creek, a perennial salmon-bearing tributary stream to Lake Washington. Taylor Creek Headwaters wetland is high-functioning, providing a range of water quality, hydrologic, and habitat functions in a moderate density urban landscape. The wetland is classified as a North Pacific Hardwood-Conifer Swamp and contains forested, scrub-shrub, and emergent wetland habitats dominated by Western red-cedar, Oregon ash and red alder. Standing snags, downed woody debris and other special habitat features in the wetland on the property provide an opportunity to support amphibians, reptiles, fish, birds, and mammals.

This property provided a rare opportunity to save a high functioning urban wetland from imminent development.


Elliott Bridge Reach Off-Channel Wetland & Floodplain Reconnection Project

Construction completed 2016

Located in the Cedar River Watershed (WRIA 8), the Elliott Bridge Reach Mitigation Project created and enhanced wetland and aquatic habitat and restored floodplain functions within the Elliott Bridge Reach of the Cedar River. The project area is approximately 11.5 acres and includes off-channel and in-channel components and riparian/floodplain type mitigation. Specific mitigation project features total more than 9 acres of restoration. Additionally, an in-stream scour structure was installed on the right bank and a portion of the rock revetment was removed.

The goal of the Elliott Bridge Reach Mitigation Project is to address needs in the Cedar River Watershed by reducing flood damage, protecting and restoring aquatic habitat, and maintaining water quality.

The majority of mitigation credit generated by the Elliott Bridge Reach Mitigation Project will offset a portion of WSDOT’s SR 520, I-5 to Medina: Bridge Replacement and HOV project.

More details on the construction of the mitigation site can be found at the Elliott Bridge Reach Project web page.


McElhoe-Pearson Off-Channel Wetland & Floodplain Reconnection Project

Construction completed 2012

Located in the Snohomish River Watershed (WRIA 7), in the Snoqualmie River Service Area, the McElhoe-Pearson Mitigation Project created additional rearing and refuge habitat for salmonid species in the Snoqualmie River and provided needed flood storage capacity. This project restored a surface water connection between the Snoqualmie River and a portion of the historic floodplain that has been isolated for over 50 years. With the reconnection, this high quality wetland is now accessible to juvenile salmonids..

500 linear feet of channel was restored. Reconnection created approximately two acres of enhanced off-channel rearing and flood refuge habitat. Construction of the McElhoe-Pearson Mitigation Site also included enhancement of the existing wetland, riparian planting, and installation of large wood.

The McElhoe-Pearson Mitigation Site was specifically constructed to offset impacts associated with WSDOT’s Tokul Creek Emergency Project, which included 15,580 square feet of permanent stream impacts, 10,986 square feet of permanent riparian impacts and the removal of large wood.

More details on the construction of the mitigation site can be found at the McElhoe-Pearson Project web page.


For questions about King County's Mitigation Reserves Program, please contact program staff.