The Columbia River Estuary encompasses more than 40,000 hectares of land. Although there are no dams on the Columbia River below Bonneville, the system has been dramatically altered by the dredging, ditching and construction of flood control levees. In addition, an extensive dam system on the lower tributaries to the Columbia River has dramatically altered natural hydrology, affecting the natural processes that form and maintain wetland habitats. The extensive loss and conversion of floodplain habitats in the lower Columbia River has not only affected waterfowl habitat, but is one of the leading factors in the decline of other species, including 12 stocks of salmonids that are listed under the Endangered Species Act.
Prior to settlement, the Willamette Valley contained extensive systems of floodplains and wet prairie wetland habitats. It is believed that between 120,000 and 160,000 hectares of wetland prairie existed in 1850. Today, less than 400 hectares remain (Guard 1995). The Willamette Valley provides wintering habitat for large number of ducks, including more than 50,000 mallards and 30,000 American wigeons. Green-winged teal, pintail and ring-necked duck are common migrants and wintering birds. Total numbers of wintering Canada geese have grown from 20,000 to more than 250,000 birds.
In coastal Oregon, mallards, northern shovelers, American wigeons, northern pintails and green-winged teal are the principle dabbling ducks, whereas, canvasbacks, ring-necked ducks, and scaup are the principle diving ducks. Scaup and ring-necked ducks are found primarily in the Columbia River estuary. During harsh winters in the Great Basin, coastal Oregon experiences a 100 to 200 percent increase in bird use. For example, scoters are common wintering birds off several estuaries. Aleutian Canada geese (more than 10,000 birds) stage on pastures along the New River and Nestucca Bay.