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Wetland mitigation resources

The state's wetland program goal is to achieve a no overall net loss in the amount (acreage) and function of Washington's remaining wetlands. The program also aims to increase the quantity and quality of Washington's wetlands resource base. We meet these goals, in part, through strategies designed to avoid, minimize and compensate or mitigate for adverse impacts to wetlands.

We provide resources to landowners and developers to help with wetland mitigation planning. 

What is mitigation?

Generally, mitigation means offsetting or countering the adverse environmental effects that developing the land can have on wetlands, rivers, streams, lakes, and other aquatic habitats. Wetland mitigation usually occurs in a sequence of steps or actions.

Wetland compensatory mitigation is one of the last steps in the mitigation sequence where unavoidable impacts to wetland functions are offset by creating, restoring, enhancing, or preserving other wetlands. Use the resources below to apply mitigation sequencing and to select, design, and implement compensatory mitigation.

Mitigation resources

Identify wetlands on the proposed development site

An on-site inspection is almost always necessary to determine, with certainty, whether wetlands are present. Other information, such as Ecology Wetland Inventory Maps, National Wetland Inventory Maps, county soil surveys, and aerial photos provide indications of where wetlands may exist. However, these might not include all wetlands and might identify areas that were once, but are no longer wetlands.

Avoid and minimize wetlands impacts

Characterize wetland functions and values

Better mitigation through a better understanding of wetland functions and values:

Identify mitigation opportunities

In addition to traditional on-site mitigation, there may be other ways to achieve mitigation depending on what can work best for the applicant and the environment. Each option must conform to appropriate local, state, and federal regulations and permits.

Understand mitigation options

Determining which mitigation option, or combination of options, is best for your site must be done on a case-by-case basis. Washington provides a comprehensive range of mitigation options:

  • Wetland mitigation banking:  A mitigation bank is a wetland, stream, or other aquatic resource area that has been restored, established, enhanced, or, in certain circumstances, preserved for providing compensation in advance of unavoidable impacts to aquatic resources.
  • In-lieu fee (ILF) mitigation: In this approach to mitigation, a permittee pays a fee to a third party in lieu of conducting project-specific mitigation or buying credits from a mitigation bank.
  • Advance mitigation: Is constructed in advance of a permitted impact. Advance mitigation can be proposed by any applicant, but the advance compensatory mitigation credits generated by a mitigation effort in advance of impacts can only be used by that same applicant. See the Interagency Regulatory Guide: Advance Permittee-Responsible Mitigation.

In some cases, it may be best to use a combination of onsite and offsite mitigation. An applicant may buy credits from a wetland mitigation bank or pay for in-lieu fee mitigation rather than mitigate for their unavoidable impacts to wetlands onsite. Or, it may be best to provide some functions like onsite water quality and quantity  and compensate for habitat functions offsite.

Choose a mitigation site

Better mitigation through improved site selection:

Develop and implement a wetland mitigation plan

Monitor mitigation site success