The Nooksack River is a river in western Whatcom County of the northwestern U.S. state of Washington, draining extensive valley systems within the North Cascades around Mount Shuksan, Mount Baker and the Twin Sisters, and a portion of Fraser Lowland south of the Canada–United States border.

Gathering meltwater off East Nooksack Glacier, it flows generally west past north of Mount Baker.

[6] The South Fork Nooksack River, about 50 miles (80 km) long, rises in southern Whatcom County, east of Twin Sisters Mountain near Bell Pass and Lake Wiseman.

[9] The river supplies the nearby town of Glacier, Washington with hydroelectric power from a dam on the North Fork near Nooksack Falls.

As of July 2020, this old water diversion system has been modified to remove the dam and restore the river channel for the benefit of critical salmon spawning habitat.

The river is subject to flooding due to high rainfall amounts in the region and some of the deepest snow packs in the country.

The Pineapple Express, a weather pattern that brings central Pacific wind and rain to the northwest, can sometimes catalyze flooding.

has been reluctant to use the International Joint Commission following a 1988 report that resulted in the cancellation of the Sage Creek coal mine on the Flathead River".