The Mattole River's mainstem is in length and has more than 74 tributaries. It has historically had large runs of salmon and steelhead trout, but due to past logging, road building and severe floods in 1955 and 1964, all of which impacted the river, fish numbers have declined.EIS-ch3,pt5,pp4-10 The coho salmon is a federally listed threatened species (Southern Oregon/Northern California populations)US Fish and Wildlife Service Species Report. accessed Feb.14, 2009 that use the Mattole River and its tributary, Mill Creek. Increased sediment and lack of tree cover reduced the quality and quantity of fish habitat by increasing summer water temperatures. The Environmental Protection Agency added the Mattole River to the state's list of impaired watersheds in 1992. Environmental Protection Agency, Mattole River document. December, 2003 accessed Feb 17,2009
