The Monument includes the Hanford Reach, the nation’s last, non-tidal, free-flowing segment of the Columbia River. Forty-three species of fish have been documented as occurring in the Hanford Reach. Salmonids are of particular interest, large numbers of fall chinook salmon (Onchorynchus tshawytscha) spawn in the Hanford Reach, Upper Columbia River Spring Chinook (Onchorynchus tshawytscha), listed as a federally threatened species, also uses the Hanford Reach for migration, as well as both the Middle Columbia River Steelhead (Onchorynchus mykiss) and Upper Columbia River Steelhead (Onchorynchus mykiss) both of which are federally threatened species. Beach seine catches from April-June in the Hanford Reach are dominated by subyearling fall chinook salmon (USGS, unpublished data). Other numerically important species during this time are redside shiners, carp, largescale suckers, northern pikeminnow, and peamouth. Mountain whitefish are common in the Hanford Reach and support a recreational fishery. Centrarchids and percids are more common in McNary Reservoir, although smallmouth bass are also abundant in the Hanford Reach. Tench, three-spine sticklebacks, and mountain whitefish are rarely captured in Hanford Reach seining activities. The ponds and lakes created by irrigation run-off also have populations of introduced fishes such as carp, bass, sunfish, and panfish. Riparian vegetation and backwater sloughs are very important for fisheries habitat. Shoreline vegetation provides shade, moderates temperatures in shallow water and provides shelter and substrate for invertebrate populations all of which are critical for sustaining fish populations. Occasionally, vegetation may become dense and limit open water habitat.
The Hanford Reach (Reach) is the last free-flowing section of the Columbia River upstream from Bonneville Dam. The Reach contains islands, riffles, gravel bars, oxbow ponds, and backwater sloughs that support some of the most productive spawning areas in the Northwest, including the largest remaining stock of wild fall chinook salmon in the Columbia Basin. The loss of other spawning grounds on the Columbia and its tributaries has increased the importance of the Reach for fisheries. The Reach is one of the primary features of the Hanford Reach National Monument, designated by Presidential Proclamation 7319, June, 2000, and administered jointly by the Department of Energy and FWS.
In July, 2000, the FWS was assigned responsibility for overseeing the interim protection of the “outstandingly remarkable” values that made the Hanford Reach of the Columbia River suitable for addition to the National Wild and Scenic Rivers System, including fall chinook salmon. Fall chinook salmon that spawn and rear throughout the Reach are of economic and cultural importance to commercial fisheries in the North Pacific Ocean, in-river commercial and tribal fisheries, and ocean and in-river sport fisheries. This stock is also a principal component of the international Pacific Salmon Treaty between the United States and Canada. Adult spawning in the Hanford Reach has ranged from approximately 20,000 to 90,000 over the last 35 years. Streamflows in the Reach are intentionally limited during fall chinook spawning season (October-November) with the stated goal of confining spawning activity to lower river elevations that can be maintained through the winter/spring incubation and emergence time period (through mid-June). Juvenile production is approximately 20-30 million individuals annually. Streamflows vary between lower, late-winter levels and higher spring freshet flows during the spring juvenile fall chinook rearing period from mid-March through mid-June. Aquatic insects, which are a critical link in the ecosystem and support the healthy fall chinook population as well as the native resident fish community, include 145 taxa.