Watersheds

The Tolt River Watershed in 2018.

The Seattle Regional Water Supply System is supplied by the Cedar River Watershed and the Tolt River Watershed. Seattle began supplying water from the Cedar River in 1901 and from the Tolt River in 1964.

These two watersheds have a combined average storage of 31 billion gallons of water. Four million gallons of this water is treated water and serves 1.5 million people in the region. The Cedar River supplies roughly 60% of the water and the South Fork Tolt River supplying the remaining 40%.

The City of Seattle owns 99.8% of the 90,638 acres above the Landsburg diversion of the Cedar River Watershed and 68.8% of the 12,009 acres above the South Fork Tolt Dam (US Forest Service owns the rest). These watersheds also serve as a home for wildlife and salmon.

Cedar River Watershed

The City of Seattle's Cedar River Municipal Watershed is carefully managed to support and supply clean drinking water to 1.5 million people in the greater Seattle area. The watershed covers 90,638 acres, hosts a rich diversity of plants, animals, and habitats, and is owned by the City of Seattle.

Tolt River Watershed

The South Fork Tolt River is the smaller and lesser known (than the Cedar River) but still essential second supply watershed in Seattle Public Utilities' freshwater supply system. Located in the foothills of the Cascades in east King County, it supplies about 30% of the drinking water for 1.5 million people in and around Seattle.

Habitat Conservation Plan

The Cedar River Watershed Habitat Conservation Plan (HCP) is a 50-year, ecosystem-based plan to address declining populations of salmon, steelhead and other fish and wildlife in the Cedar River basin. The HCP is designed to protect and restore habitats for 82 species of fish and wildlife and mitigate for drinking water withdrawals through applying the latest scientific knowledge.