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Landsburg Mitigation
History of the Landsburg Fish Passage
The Landsburg Diversion Dam on the Cedar River has blocked fish passage into the upper watershed since 1901. The dam was built to provide a reliable supply of water to the City of Seattle and surrounding communities. The Cedar River provides 2/3 of the drinking water for 1.3 million people. The dam does not store water; rather it regulates the amount of water that is sent to the Lake Youngs Reservoir through a 96” diameter aqueduct. Of the total instream flow in the Cedar River, 18% - 20% of the average annual flow is diverted to Lake Youngs.
In the year 2000, the City of Seattle signed the Cedar River Habitat Conservation Plan (HCP), a 50-year, ecosystem-based plan that contributes to the recovery of populations of salmon, steelhead and other species of fish and wildlife in the Cedar River basin. In 2003, the City of Seattle completed a major milestone of the HCP: the construction of fish passage facilities at Landsburg for Chinook, coho, and steelhead trout. The main components of the fish passage facilities are:
- • two fish ladders (one at the dam and one at the Lake Youngs aqueduct crossing)
- • a fish screen at the water supply intake
- • modifications to the dam (a tip out gate and plunge pool to protect downstream migrating juvenile fish).
These improvements restored 12.5 miles of mainstream habitat and approximately 4.5 miles of tributary habitat for Chinook, coho, and steelhead trout. Sockeye are not allowed to pass above Landsburg because of the concern that large numbers of spawning salmon could adversely affect drinking water quality.
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