The Nooksack watershed covers over 830 square miles in northwestern Washington and British Columbia. The middle fork of the Nooksack River begins at Mount Shuksan, in North Cascades National Park, and the north and south forks flow from Mount Baker, at 10,778 feet, and Twin Sisters Mountain. Glacier melt, snowmelt, groundwater, and rainfall feed the 1,400 stream and river miles that comprise the watershed. Most of the upper watershed is federally owned, but the middle section consists of private land, state land, and small landowner forestry operations. The lower portion of the watershed is still fairly rural, but more heavily developed than the upper reaches, with farms and residences dominating the landscape.
The river eventually drains to Bellingham Bay, through one of the highest quality estuaries in the Sound. Salmon utilize the nearshore habitat, although sediment in the river proves challenging both for human occupants and fish. The upper watershed is prone to landslides, and land management has increased sediment runoff. In some areas, the river channel migrates frequently during winter floods, which can wash away salmon eggs and reduce habitat for young fish. In addition, the South Fork has lower water flow and more mixed land use surrounding it, which often leads to temperatures too high for Chinook salmon. Nooksack Chinook are listed as threatened under the Endangered Species Act.
- Counties: Skagit, Whatcom
- National Estuary Programs: Puget Sound
- Other Watersheds Upstream: Fraser, Puget Sound
- Other Watersheds Downstream: Strait of Georgia