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Instream Flow photo identifier

Instream Flow

Instream Flow Home photo

Ecology is required by state law to retain adequate amounts of water in streams to protect and preserve instream resources and uses (such as fish, wildlife, recreation, aesthetics, water quality and navigation).  One of the best water management tools for protecting stream flows is to set flow levels in regulation.  Specific stream flow amounts protected in a regulation are called “instream flows.”

Both the natural environment and our community water supplies rely on healthy stream flows.  Yet many streams around the state are often below critical levels. Some streams have dropped to historic lows.  Population growth and reduced snowpack continue to put more stress on this finite resource.  No new water is being made!

Watershed management groups around the state are examining local water resources and many are working with Ecology to set or revise instream flows in their watersheds.  The intent is to set instream flows throughout the state.  More information

Setting flows does not put water in streams, and does not affect existing (senior) water rights.  Instream flows protect the river from future withdrawals.

Introduction to Instream Flows and Instream Flow Rules Introduction to Instream Flows and Instream Flow Rules
Answers to your basic questions, including: What is an instream flow?  Why are stream flows important?  What is an instream flow rule?  How could setting instream flows affect me?
The Science Behind Instream Flows The Science Behind Instream Flows
How do we determine instream flow levels?  We start with fish habitat studies, such as Instream Flow Incremental Methodology (IFIM) and Toe-width.
Instream Flow Setting Around the State Instream Flow Setting Around the State
Where can I get more information about my watershed, including whether instream flows have been set?
Laws and Rules Laws and Rules
A look at the legal authority to set instream flows by rule and the complex process of developing instream flow/water management rules.
Resources and Studies Resources and Studies
Want to know more?  Here are links to IFIM studies, publications and other resources.



Technical or scientific questions about instream flows:
Jim Pacheco
Department of Ecology, HQ
(360) 407-7458

Policy and instream flow rule questions:
Ann Wessel
Department of Ecology
(360) 715-5215




Video is window on how your water resources are managed




Instream flow data are provided to inform the public about the amount of water available in the streams and rivers they rely on.

ECOLOGY'S STATEWIDE FLOW MONITORING NETWORK - see nearly real-time summaries of streamflow around the state.


Development and Implementation of Watershed Plans