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Lake Terrell and Tennant Lake Wildlife Area Fish Passage and Diversion Screening Prioritization Inventory

Category: Habitat - Fish Passage Technical Assistance

Date Published: July 2003

Number of Pages: 30

Author(s): Laura Till and Dave Caudill


The Washington Department of Fish and Wildlife (WDFW) is committed to providing leadership in restoring salmon and trout (salmonid) populations in Washington State. WDFW conducts Fish Passage Barrier and Surface Water Diversion Screening Assessment and Prioritization projects, which address two factors limiting salmonid populations:

  • Human-made barriers to fish passage such as culverts and dams
  • Salmonid mortality from unscreened or inadequately screened water diversions

When culverts and dams are barriers to fish migration, productive habitat becomes inaccessible. Both adult and juvenile salmonids need to move freely up and downstream to find suitable spawning gravel or disperse from the redd into rearing habitat. Even resident trout need full access to all habitat types to spawn, rear, maximize genetic interchange and survive varying flow conditions.

Juvenile mortality occurs in unscreened or inadequately screened diversions. Water diversion ditches resemble side channels in which juvenile salmonids normally find refuge. However, when diversion headgates are shut, access back to the main channel is cut off and the channel goes dry. Mortality can also occur with inadequately screened diversions from impingement on the screen, or mutilation in pumps where gaps or oversized screen openings allow juveniles to get into the system.

Inventories of fish passage barriers and water diversions are being conducted on each of the Wildlife Areas owned or managed by WDFW. The inventories and habitat surveys document and prioritize for correction all human-made fish passage barriers and unscreened or inadequately screened diversions to ensure compliance with Washington State laws (RCW 77.55.060, RCW 77.55.040).

For this report, the location of a fish passage or safety structure is referred to as a site. The structure at that site is referred to as a feature.

Features affecting fish passage include:

  • Culverts
  • Dams
  • Fishways

Features affecting fish safety include:

  • Gravity diversions
  • Pump diversions

A site may have one or more features associated with it such as a gravity diversion with a dam to impound water and direct it to the diversion. A dam may be equipped with a fishway to facilitate fish passage around the dam.

This report summarizes the results of the Lake Terrell and Tennant Lake Wildlife Area inventory with preliminary plans and recommendations to correct the problems identified.