Protecting stream flows

What is an instream flow rule? 

An instream flow rule is an administrative rule adopted by Ecology that identifies minimum flow levels for regulatory action. When actual flows fall below the minimum flow levels identified in rule, Ecology requires water users that are junior to (issued after) the adopted flows to curtail use. Through this action, Ecology can protect remaining flows from being used for other out-of-stream purposes. 

How do instream flow rules work? 

Instream flow rules function like a water right for the river. In Washington, water rights operate on the basis of seniority. Once adopted, instream flows identified in rule must be satisfied before any newer (“junior”) water users can use water for out-of-stream purposes. Water right permit applications that require continuous use of water (such as municipal drinking water) will be denied if that water use would impair adopted instream flows. Senior water users, or water right holders whose water rights pre-date the instream flow rule’s adoption, are unaffected and may continue to use water. 

Minimum flow levels identified in rule do not guarantee that a certain flow will be present in the river. Actual stream flow (i.e., the water in a stream at any one time) may fall below regulatory minimum flow levels due to natural variability, as well as use of water by senior water right holders.  

When actual stream flow is below the level in an instream flow rule, that does not mean the stream is impaired, nor does it mean the rule is failing to protect the river. The flow levels adopted in an instream flow rule represent flows that maximize available fish habitat and other instream resources, even if those adopted flow levels only occasionally occur. 

• Watch a video about instream flows 

Streamflow restoration 

Ecology also provides funding for streamflow restoration projects that protect and enhance streamflows through its Streamflow Restoration Grant Program. Many projects funded through these programs are water right acquisitions that are placed in the Trust Water Rights Program and protected for instream use. To learn more about these programs, visit the links below: 

• Streamflow Restoration 

• Trust Water Rights Program 

Groundwater use 

Most groundwater in Washington is hydrologically connected to some extent to surface waters, such as wetlands, lakes, and streams. As a result, groundwater pumping can decrease streamflow in nearby surface water bodies. Therefore, instream flow rules also apply to groundwater uses if there is any connection to regulated surface waters.