In late 2000, a lawsuit was filed challenging the NOAA Fisheries Service February 2000 final designation of critical habitat for 19 populations, or evolutionarily significant units (ESUs), of Pacific salmon and steelhead listed under the Endangered Species Act (ESA). A federal court ruled that the agency did not adequately consider the economic impacts of the critical habitat designations.

In April 2002, NOAA Fisheries Service withdrew its 2000 critical habitat designations. Another lawsuit was filed, alleging that the agency failed to designate critical habitat in a timely manner for the 19 ESUs for which critical habitat had been vacated (and for a recently listed species, northern California steelhead). NOAA Fisheries Service entered into a settlement under which the agency agreed to file final critical habitat designations by Aug. 15, 2005, for those of the 20 ESUs listed as of that date.

The agency announced its final critical habitat designations for 19 ESUs on Aug. 12, 2005. (The Oregon coast coho ESU was proposed for listing at that time, so wasn't included.) Federal Register notices on these designations published Sept. 2, 2005. They became effective Jan. 2, 2006.

Final critical habitat designated before 2000 for six listed ESUs has remained in place: Snake River sockeye; Sacramento River winter-run, Snake River spring/summer-run and fall-run Chinook; and central California coast and southern Oregon/northern California coho.