Beaver ponds most commonly occur in mid-elevation, montane valleys where the slope is <15%. Because beaver ponds are often clustered in "flowages" along suitable lengths of streams and rivers, they provide a valuable wetland community well suited to the needs of breeding waterfowl. Densities of 5 to 10 ponds/km of stream are common, increasing to as many as 42 ponds/km in excellent habitat with high beaver populations. Wetlands created by beaver possess relatively stable water levels maintained by precipitation and runoff. However, beaver flowages themselves may be somewhat ephemeral in nature, and usually are abandoned within 10-30 years, after beaver deplete their food resources. Beaver ponds act as nutrient sinks by trapping sediments and organic matter that otherwise would be carried downstream. This function enhances wetland fertility and the plant and aquatic invertebrate communities exploited by waterfowl. Invertebrates typical of running water systems are replaced by pond organisms such as snails, freshwater shrimp, and the larvae and immature stages of caddisflies, dragonflies, flies, and mosquitoes. Structural cover provided by flooded willows, alders, sedges, burreeds, and other emergents affords ideal habitat for waterfowl breeding pairs and broods.
Glacial ponds include both small wetlands formed behind lateral and terminal moraines of glaciers, and "kettle ponds" created by the same glacial process that formed the prairie "potholes"—ice embedded in glacial till melted after glaciers retreated, forming depressions that later filled with water. Glacial wetlands most commonly occur in mountainous terrain. Often, these ponds are dependent solely on spring runoff and summer precipitation for water. Therefore, water levels recede during summer, while density and abundance of herbaceous, emergent vegetation increases. Despite dynamic water levels, natural succession is slow. Peat accumulations indicate that some glacial ponds have persisted as wetlands for >7,000 years. Northern mannagrass, sedges, and reedgrasses are common emergent plants in these wetlands, as are submerged species such as pondweeds, watermilfoils, and cowlilies. Often, the size and physical setting of glacial ponds restrict waterfowl use to dabbling ducks, which can land and takeoff in confined areas. The shallow water of these ponds is unsuitable for sustaining fish populations, which might otherwise compete with waterfowl for aquatic invertebrate foods. The abundant plant and animal foods in glacial ponds make these wetlands very attractive to waterfowl.
The headwaters of many major river systems begin in the RCP. At high and mid-elevations, these streams and rivers often flow unrestricted by major dams and diversions. Accordingly, overbank-flooding wetlands develop along riparian corridors during spring runoff, creating potential habitat for waterfowl. Unfortunately, the timing of runoff, from late April and May in Lower and Upper Montane Zones to June and early July in Subalpine areas, may actually be detrimental to waterfowl nesting along river margins or on islands in the main channel. It is not unusual for nests of ducks and geese to be flooded by runoff. Nonetheless, the backwaters, sloughs, and old oxbows associated with western riparian areas provide important benefits to waterfowl during spring and fall migration, and for waterfowl that select nesting sites on higher ground away from flood-prone areas.
Other riverine systems in this region have been negatively impacted by significant man-made alterations, including dams and flood control levees. Most of this alteration was implemented to improve agricultural viability within the region by storing water for irrigation and preventing flooding of croplands and haylands. While these alterations to natural hydrology have negatively impacted waterfowl habitat, many of these systems continue to provide important resources to waterfowl and offer ideal locations to focus habitat conservation activities. The Baker Valley and Lower Powder River Valley in Baker County, Oregon provide significant resources to spring migrating waterfowl and have been the focus of several conservation projects. The Grande Ronde Valley in northeast Oregon is the home of the Ladd Marsh Wildlife Area. Several projects have been completed, or are underway, in this area. Combined, these projects will restore approximately 506 ha of wetland habitat, providing significant benefits to both migrating and locally breeding waterfowl. The Kootenai River valley in the Idaho panhandle is another floodplain system that has been extensively altered by levee construction. Several projects have been completed to restore over 405 ha of wetland habitat in this area.