Instream flow & water management rules

Rule implementation activities 

In basins where instream flows are adopted, Ecology partners with watershed partners to effectively implement these regulations. For more information on recent instream flow implementation activities, see the webpages for individual basins linked below: 

• Dungeness River basin  
• Nooksack River basin 
• Skagit River basin  
• Spokane River and Rathdrum Prairie Aquifer  
• Stillaguamish River basin 

How are instream flow levels set? 

Setting instream flow levels in rule is a complex process, involving: 

• Scientific flow studies to determine what flow levels are needed to preserve the uses and values of individual rivers and streams. 

• Developing methods to minimize the impacts of future development. 

• Working with local agencies, tribes, businesses, environmental groups, and concerned citizens throughout the rule development and adoption process. 

Related case law 

The Washington State Supreme Court has issued a number of decisions affecting management of instream flow rules and related water resource management. These include: 

• Foster v. Ecology (2016): Prohibits out-of-kind mitigation and limits Ecology’s authority to authorize new water rights based on the overriding consideration of public interest standard. 

• Whatcom County v. Hirst (2015): Requires counties to independently determine water availability under the Growth Management Act when approving permit-exempt water uses. These requirements were subsequently modified by the passage of the Streamflow Restoration Act (chapter 90.94 RCW) by the Legislature in 2018. 

• Postema v. PCHB (1999): Clarifies that even very small (“de minimis”) impacts to instream flows are not authorized, including impacts caused by hydrologically connected groundwater. 

• Swinomish v. Ecology (2013): Restricts Ecology’s authority to establish reserves of water for new out-of-stream uses based on overriding consideration of the public interest. 

See more information: 

• An introduction to: Instream flows and instream flow rules 
• Instream flow study methods used in Washington State 
• Instream flow study guidelines: Technical and habitat suitability issues