Wetland mitigation

Wetland mitigation compensates for adverse effects projects have on wetlands, streams, lakes, and other aquatic resources. If a construction project has adverse effects on wetlands after avoiding and minimizing impacts through alignment and design, then mitigation is required.

This page contains technical information to complete every stage of wetland mitigation for your project:

Our Wetlands Protection and Preservation policy (pdf 47 kb) directs Washington State Department of Transportation (WSDOT) staff to protect and preserve wetlands, ensure no net loss of wetland acreage and functions, and increase the quantity and quality of wetlands in the long term.

Read Chapter 431: Wetlands of our Environmental Manual for policies related to assessing wetlands and other waters, determining impacts (adverse effects), and mitigating for unavoidable impacts.

Understand mitigation options

WSDOT may have credits available from a constructed advance mitigation site or a WSDOT mitigation bank. Always consider existing mitigation bank and in-lieu fee credits before developing WSDOT designed mitigation.

Visit the Department of Ecology’s (Ecology) Mitigation Options page for an overview of other mitigation options available.

Identify mitigation requirements

Begin the mitigation process by identifying the extent of wetland and wetland buffer impacts and determine the size and type of mitigation required.

Use available WSDOT mitigation credits

When available, use existing WSDOT mitigation credits. Determine if appropriate existing credits are available to compensate for the proposed impact of your project from either existing credit from an approved advance mitigation site or credit from a WSDOT mitigation bank.

Contact Gretchen Lux, Gretchen.Lux@wsdot.wa.gov, to determine if one of WSDOT’s three certified mitigation banks has credits appropriate for your project:

Purchase mitigation credits

Purchasing mitigation credit from a certified non-WSDOT mitigation bank or In-Lieu Fee (ILF) program may be a cost-effective option. With this approach the mitigation bank or ILF sponsor is responsible for all aspects of the mitigation site instead of WSDOT.

The project impact needs to be within the mitigation bank or ILF’s service area. The bank or ILF must have sufficient available mitigation credits to compensate for the project impact.

Ecology’s website on ILF mitigation includes a list of bank providers. Contact the bank or ILF sponsor directly to determine the availability of credits.

To ensure compliance with applicable procurement laws and to limit liability, follow our Environmental Mitigation Credit Procurement Process (pdf 64 kb)  to get credit from non-WSDOT entities. Use the Environmental Mitigation Credit Standard Form Agreement (docx 75 kb) to purchase environmental mitigation credits from a certified mitigation bank.

Select a mitigation site

When there are no WSDOT established mitigation credits, suitable private non-WSDOT mitigation banks, or ILF credits available, WSDOT must develop a permittee-responsible mitigation site. In this case your project must establish a mitigation site. Initiate your site selection process after you have identified preliminary mitigation requirements and have determined the mitigation goals. Consider early coordination with regulatory agencies when developing mitigation strategies for complex projects. Incorporate considerations in Avoiding Impacts to Agricultural lands of Long-Term Significance (pdf 45 kb) and the associated Directional Memo (pdf 254 kb). into the mitigation strategy.

Collect mitigation site data

After identifying the mitigation site and initiating the property acquisition, begin collecting on-site data for the wetland mitigation design and report. 

  • Conduct on-site vegetation, soil, and hydrological surveys using the directions provided on our Wetland reconnaissance and assessment page.
  • If wetlands are already present on the mitigation site, a memo is required.

For detailed guidance on mitigation site selection and design, contact the Wetland Program Manager

Prepare the Wetland and Stream Mitigation Report

When you have collected all required mitigation site data, write the Wetland and Stream Mitigation Report (doc 983 kb) to compile your design.

Submit the report as part of your project’s Joint Aquatic Resource Permit Application (JARPA). Find more information on our  JARPA page.

Establish performance criteria

Performance standards describe measurable features used to evaluate compensatory mitigation sites. Performance standards are approved during the permitting process and must be included in the Wetland and Stream Mitigation Report. WSDOT monitors mitigation sites for up to ten years to ensure the site meets performance standards. 

Initiate monitoring coordination

Monitoring activities may need to begin before mitigation site construction starts. Follow the instructions on our Wetland monitoring page to start the mitigation site monitoring process.

Mitigation site construction

After the mitigation site is designed and permitted, the next stage is to construct the site. See our Wetlands construction web page for important information about how to limit impacts to wetlands during construction.