Landsburg Fish Passage

From 1901-2003, the Landsburg Diversion Dam and a water supply aqueduct were barriers to salmon and other migratory fish species in the Cedar River. Fish access and fish-friendly water system improvements were added in 2003 as part of the Habitat Conservation Plan and the Landsburg Mitigation Agreement. Over 17 miles of high quality mainstem and tributary habitat in Seattle's Municipal Watershed and this work has been a key component of salmon recovery efforts in the Lake Washington Basin.

Seattle Public Utilities (SPU) continues to monitor the timing, species, and count of fish utilizing the fish ladder with a river camera system and also monitors fish habitat by conducting redd surveys along the mainstem Cedar above the Diversion Dam when salmon are spawning. Monitoring suggests that fish are performing well in this new habitat and both coho and Chinook salmon have successfully recolonized above the Diversion Dam.


Seattle Public Utilities and the Anadromous Fish Committee oversee facility improvements and fish passage facility operations.

Photo of the Cedar aqueduct in 2003
Cedar aqueduct prior to boulder additions (2003)
Photo of the Cedar River with boulders
Boulders were added to the Cedar River to create a fish-friendly set of rapids and pools over the aqueduct.

Photo of a Diversion Dam gate
A gate in the Diversion Dam was replaced to allow water and fish migrating downstream to spill over the top.
Photo of the fish ladder
A fish ladder was added to provide year-round upstream passage around the Diversion Dam for coho, Chinook, steelhead, lamprey, trout and other migratory species. Because of their much higher numbers, sockeye can pose a risk to drinking water quality and are not passed above the dam. Sorting facilities at the ladder allow the exclusion of sockeye from above the dam.

Screens were added to the municipal water intake to redirect downstream migrating fish back into the river.

Graphic of the screens at the dam

 

Salmon in the Cedar River Watershed

SPU, NOAA Fisheries, and University of Washington scientists monitored the fish population above the Landsburg Diversion Dam before and after the fish passage projects were completed to determine whether the fish population, fish habitat use, and water quality had changed with the presence of salmon.

Scientists PIT tagged fish to track movements, snorkeled mainstem Cedar and tributaries to determine juvenile fish abundance, quantified available fish habitat by measuring logs, in-stream habitat, algae growth and invertebrates, collected water samples for nutrient analyses, and collected fish tissue for genetic studies.

Key results

Graphic of fish densities
Salmon + trout densities before (2000-2002) and after (2004-2005) installation of the Landsburg fish passage facility. Modified from Kiffney et al. 2007.
  • After completion of the fish ladder, large numbers of juvenile salmon were recorded within 5 km upstream of the Diversion Dam
  • Side channels had the largest densities of juvenile coho, Chinook and trout. (Kiffney et al. 2007)
  • There have been no significant changes to water quality (Herrera 2007)
  • Variation in fish density correlated with water temperature, maximum pool depth and wood abundance. (Kiffney et al. 2007)
  • From 2003-2019, over 7,459 coho, 3,114 Chinook, and 24 steelhead have passed above the Diversion Dam.

 

Photo of a salmon

Fish Passage: Who's on the Move?

The species and number of fish migrating above the Landsburg Diversion Dam are counted throughout the year. A camera at the upstream end of the fish ladder is used to identify and count of fish from November through August. During the peak migration of sockeye salmon in September and October, the all fish entering the ladder are sorted by hand; sockeye are sorted out and all other species (e.g. coho and Chinook salmon, trout, whitefish) are carried upstream of the Diversion Dam and released into the forebay.

When fish are handled, the species, sex, origin (natural or hatchery) and length are recorded. Reports are produced annually.