Regulations, guidelines, and determining compliance

The Revised Code of Washington states that all water diversion devices must have compliant fish screens. We can clarify how these regulations apply to your water diversion. We can also assess whether your screen is in compliance with regulations.


  • RCW 77.57.010 - Fish guards required on diversion devices--Penalties, remedies for failure.
  • RCW 77.57.040 - Director may modify inadequate fishways and fish guards.
  • RCW 77.57.070 - Diversion of water--Screen, bypass required.


Determining compliance

Compliant fish screens draw water across the entire screening surface. This eliminates the “hot spots” of stronger suction that can occur with non-compliant screens and ensures fish are not trapped by the suction (impinged) and harmed.

How is fish screen compliance determined?

WDFW evaluates many factors to determine screen compliance, including:

Velocity: When choosing a fish screen for a site, we consider the swimming ability of fish. There are two important velocity factors:

  1. Approach velocity - water flowing perpendicular to the screen face.
  2. Sweeping velocity - water flowing parallel to the screen face.

Screen material: Screening requirements are established based on fry-sized (very young) salmonids. The maximum opening size differs for each screen material.

Fish bypass: Bypass systems are used with modular screens and are designed to guide fish away from the screen and back to the stream or river.

Screen condition: WDFW assesses screen degradation by checking seals, looking for damage, and examining the screen for clogged areas.