Previously, NMFS completed a comprehensive status review of west coast steelhead (Oncorhynchus mykiss) populations in Washington, Oregon, Idaho, and California, and identified 15 Evolutionarily Significant Units (ESUs) within this range. NMFS now issues a final rule to list two ESUs as threatened under the Endangered Species Act (ESA). The listed ESUs include the Middle Columbia River ESU located in Washington and Oregon, and the Upper Willamette River ESU located in Oregon. In both threatened ESUs, only naturally spawned populations of steelhead residing below impassable natural barriers (e.g., long- standing, natural waterfalls) are listed. NMFS examined the relationship between hatchery and natural populations of steelhead in these ESUs and determines none of the identified hatchery populations are essential for recovery at this time. At this time, NMFS is listing only anadromous life forms of O. mykiss. NMFS will issue any protective regulations deemed necessary under section 4(d) of the ESA for the listed ESUs in a separate rulemaking. Even though NMFS does not now issue protective regulations for these ESUs, Federal agencies are required under section 7 of the ESA to consult with NMFS if any activity they authorize, fund, or carry out may affect listed steelhead.