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 1.6 million people in and around Seattle.

The system first came on-line in 1964, and since 1989 has also supported a small Seattle City Light hydro-electric facility. In 1997, the City of Seattle successfully exchanged lands within the South Fork Tolt watershed with Weyerhaeuser Company, giving Seattle 70% ownership (approximately 8,400 acres) of the land that supplies the water. The eastern 30% lies in the Mt. Baker-Snoqualmie National Forest.

South Fork Tolt Municipal Watershed Management Plan

Seattle Public Utilities (SPU) began collecting data and evaluating needs for a landscape management plan for the Tolt watershed upstream of the Tolt dam in 2006. Eight technical staff work groups were formed to identify issues of concern and evaluate opportunities for management actions. These groups worked together to craft the South Fork Tolt Watershed Management Plan. The final plan was approved by SPU in 2011.

Implementation of the plan is now underway, largely focusing on near-term road system improvements, small aquatic habitat restoration projects, and initiating the plan's long-term forest habitat management program. The final SFTMW Management Plan and all map appendices may be downloaded below.

South Fork Tolt Municipal Watershed Management Plan (PDF)

Further information about the plan, or requests for CD or hard copy versions of the plan and maps should be directed to Brent Lackey, Major Watersheds Strategic Advisor, at (206) 684-7890 or

Tolt II Pipeline

In order to improve our ability to continue to meet the needs of an ever-growing eastside community, Seattle Public Utilities (SPU) constructed a second, larger pipeline from the South Fork Tolt River Watershed to the SPU supply distribution system. This pipeline allows SPU to more dynamically manage the balance of supply provided by the Cedar and the Tolt Watersheds, improving our capacity to react to storms or droughts, and making maintenance or repair of system components more effective. It is just a piece of the puzzle of water supply, and along with the Tolt Filtration Plant, increases our ability to meet the long-term water supply needs of the greater Seattle area with the resources of the South Fork Tolt River Municipal Watershed supply system.

Public Utilities

Andrew Lee, General Manager and CEO
Address: 700 5th Avenue, Suite 4900, Seattle, WA, 98104
Mailing Address: PO Box 34018, Seattle, WA, 98124-5177
Phone: (206) 684-3000

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Seattle Public Utilities (SPU) is comprised of three major direct-service providing utilities: the Water Utility, the Drainage and Wastewater Utility, and the Solid Waste Utility.