The Sauk River watershed reaches into Chelan, Skagit and Snohomish counties and includes parts of the Mt. Baker-Snoqualmie National Forest, the high Cascades and the Glacier Peak Wilderness. The Sauk River feeds into the Upper Skagit River, and is a popular destination for backpackers, sport fishermen and white water rafters. The river is a spawning ground for all five species of the region's salmon, and is home to bull trout, steelhead, rainbow and cutthroat trout. Megafauna may include the Grizzly Bear, with a sighting of the species recorded in the Glacier Peak Wilderness in 1996.
- Counties: Chelan, Skagit, Snohomish
- National Estuary Programs: Puget Sound
- Other Watersheds Upstream: None
- Other Watersheds Downstream: Upper Skagit