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Skip Navigation LinksDepartment of Commerce / Services & Assistance / Local Government / Growth Management Services / Growth Management Planning Topics / Critical Areas and Best Available Science

Critical Areas and Best Available Science


Since the GMA was adopted, a first step in establishing comprehensive plans and development regulations included designating and protecting critical areas. This foundational step in planning for land use in our state is based on the importance of these critical areas in supporting and protecting human life and safety, and in contributing to our high quality of life. The importance of protecting critical areas is also why this requirement applies to all jurisdictions in Washington state, even those not considered as "fully planning" under the GMA.

 Critical areas include the following areas and ecosystems: wetlands, areas with a critical recharging effect on aquifers used for potable water, fish and wildlife habitat conservation areas, frequently flooded areas, and geologically hazardous areas. All critical areas must be designated and their functions and values protected using the best available scientific information - known at best available science or BAS. As salmonid fish species play an extremely important role in the ecosystem and are vital cultural resources, jurisdictions must also "give special consideration to conservation and protection measures necessary to preserve or enhance anadromous fisheries." [RCW 36.70A.172 (1)]

Critical areas occur throughout the state, in locations that are both known and unknown. Locally adopted criteria are used to determine the presence or absence of critical areas during land development permit application reviews. Many jurisdictions map known critical areas.

 Protecting critical areas has a nexus in several federal and state laws: including the Federal Clean Water Act, Safe Drinking Water Act, Endangered Species Act, the National Environmental Policy Act, and the National Floodplain Insurance Program (administered by FEMA); and including the Washington State Environmental Policy Act (SEPA), Shoreline Management Act, Watershed Planning Act, Salmon Recovery Act, the Municipal Water Law and the GMA.  




Growth Management Services provide technical assistance through detailed guidebooks and other publications to assist local governments in planning:

Growth Management Services Guidebook: Critical Areas Assistance Handbook and Appendices: 


Critical Areas Assistance Handbook : Protecting Critical Areas within the Framework of the Washington Growth Management Act, 2003 - to help Washington communities design locally appropriate programs for designating and protecting Critical Areas.


 View Critical Areas Assistance Handbook sections :

Appendix A: Sample Code Provisions  

Appendix B: Critical Areas Update Checklist

Appendix C: Findings of Fact

Appendix D: Threatened Endangered Species

Appendix E: Priority Habitats 

Appendix F: Critical Areas Identification Form Outline 

Appendix G: Nonregulatory Protection Program

Appendix H: Nearshore Roadmap

Appendix I: GeoHaz Review Checklist

Appendix J: DNR Natural Heritage Program and Rare Plant Species Lists


GMS Guidebook: Periodic Update Process Under the Growth Management Act


GMS Guidebook: Citations of Recommended Sources of Best Available Science (BAS) – For Designating and Protecting Critical Areas


State Agency Resources for Local Governments Updating Critical Areas Ordinances:


Critical Areas Checklist Questions Explained

Critical Areas Review for Best Available Science (BAS)

GMA Update - State Agency Resources for Local Governments Updating CAOs 

 Local Critical Areas Examples:


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