Before 1850, an estimated 16 million salmon and steelhead returned to the Columbia River Basin annually to spawn. Over the past 25 years, the number of salmon and steelhead returning to the Columbia River Basin has averaged only 660,000 per year although annual population levels have varied widely. Factors such as over-harvesting, construction and operation of dams, degradation of spawning habitat, increased human population, and unfavorable weather and ocean conditions have contributed to the long-term decline. The population decline has resulted in the listing of 12 salmon and steelhead populations in the basin as threatened or endangered under the Endangered Species Act. Once a species is listed as threatened or endangered, the act requires that efforts be taken to allow its recovery. Eleven federal agencies are involved with salmon and steelhead recovery efforts in the Columbia River Basin. The National Marine Fisheries Service (NMFS), as the lead agency, is responsible for preparing a recovery plan and consulting with the other federal agencies on their planned actions. The 11 federal agencies estimate expenditures of $1.8 billion from fiscal year 1982 through fiscal year 1996 and $1.5 billion from fiscal year 1997 through fiscal year 2001 on efforts specifically designed to recover Columbia River Basin salmon and steelhead. In addition to the $1.5 billion, the 11 federal agencies estimated that they expended $302 million in the last five fiscal years on modifications to mission-related projects that benefited, but were not specifically directed at, salmon and steelhead, such as erosion control to improve crop productivity and wildlife habitat, which also improves stream flows and reduces sedimentation in spawning habitat. Although federal agencies have undertaken many types of recovery actions, there is little conclusive evidence to quantify the extent of their efforts on returning fish populations. Recovery actions taken include projects, such as constructing fish passage facilities at dams; research studies, such as determining the presence or absence of toxic substances that cause diseases in fish; monitoring actions, such as surveying spawning grounds; and other activities, such as consultations required by the act.