We, the National Marine Fisheries Service (NMFS), issue a final rule to designate critical habitat for the southern Distinct Population Segment (DPS) of Pacific eulachon (Thaleichthys pacificus), pursuant to section 4 of the Endangered Species Act (ESA). We designate 16 specific areas as critical habitat within the states of California, Oregon, and Washington. The designated areas are a combination of freshwater creeks and rivers and their associated estuaries, comprising approximately 539 km (335 mi) of habitat. The Tribal lands of four Indian Tribes are excluded from designation after evaluating the impacts of designation and benefits of exclusion associated with Tribal land ownership and management by the Tribes. No areas were excluded from designation based on economic impacts. This final rule responds to and incorporates public comments received on the proposed rule and supporting documents, as well as peer reviewer comments received on our draft biological report and draft economic report.