The Chinook or King salmon is the largest of the Pacific salmon. They can be identified by the irregular spotting and their black gums. Two genetically distinct, native species enter the Nooksack beginning in March and spawn August through early October. The North Fork run spawns in the North and Middle forks, and the South Fork stock in the South Fork. In addition, a fall chinook run (mostly nonnative) spawns in the Nooksack from September through November. All three stocks are listed as threatened under the Endangered Species Act. All runs require deeper pools and larger gravel for spawning as well as shaded riparian areas to keep the water temperatures cold in the upper reaches of the river.