The U.S. Fish and Wildlife Service (USF&WS) report said that for bull trout habitat, dam operators were likely to incur more than half of the total costs as they pay for improved fish passage and give up hydro generating capacity to boost in-stream flows. The running costs of flood control dams operated by the U.S. Army Corps of Engineers on the Willamette river in Oregon alone is expected to climb by more than US$4M a year.

The economic impact report could lead the federal government to reduce some of the stretches of stream habitat originally designated as critical for sustaining the threatened species in Oregon, Washington, Idaho and Montana.

Under the Endangered Species Act, the secretary of the interior has the authority to exclude lands from the habitat designation after weighing the costs against potential benefits for a listed species.