Complex sentence: Native fish species include Chinook and Coho Salmon, Steelhead Trout, Cutthroat Trout, Pacific Lamprey, and Rainbow Trout, but since 1922 the headworks dam has blocked anadromous fish passage to the upper river and its tributaries.
Split into simpler sentences: Native fish species include Chinook and Coho Salmon, Steelhead Trout, Cutthroat Trout, Pacific Lamprey, and Rainbow Trout. After 1922 the headworks dam blocked anadromous fish passage to the upper river and its tributaries.