Steelhead are rainbow trout that spend part of their life cycle in marine environments. Unlike other salmonids, steelhead can spawn more than once. Spawning steelhead can be identified by the pink to red striping along their sides. Four separate steelhead stocks are found in the Nooksack region. Three are native winter stocks found on each fork of the Nooksack and the fourth is the summer stock of the upper South Fork. Steelhead are listed as threatened under the Endangered Species Act.