Semi Permanent Open Water Wetlands

Ruddy Ducks depend upon Palustrine Open Water/Emergent Marsh

Open water wetlands are used for foraging, breeding, nesting and over-night staging areas for a wide variety of birds.


This habitat type, measuring between 2,200 and 2,800 acres, is primarily provided in wetland impoundments in the Blitzen Valley and Double-O units. Palustrine open water habitats are semi permanently flooded at depths that preclude the development of extensive stands of emergent vegetation. Extensive areas of emergents occur in larger impoundments. The aquatic beds of these impoundments support submerged and floating plants including common and greater duckweed; Canadian waterweed; coontail; water milfoil; common bladderwort; white water crowfoot; and sago, longleaf, and small pondweeds. Emergent plants occupy shallow areas within and alongside of open water communities and include bulrushes, cattails, sedges, rushes, and spike rushes.

These impoundments are the primary habitat for breeding and foraging of the Refuge’s population of trumpeter swans. The impoundments provide brood water for late-nesting ducks, such as redheads and gadwalls, and provide overwater nesting substrate for a large variety of wetland birds, including Canada geese, diving ducks, mallards, ruddy ducks, American coots, rails, grebes, and colonial species such as white-faced ibises and Franklin’s gulls. They also provide foraging habitat for migrating waterfowl and serve as night roosts for staging sandhill cranes and Canada geese. They serve migrant shorebirds when they are being flooded or drawn down and provide very shallow or moist mudflats. 

Muskrats use the emergent marsh component of this habitat for their lodges. Their lodges are also used by mink, which hunt muskrats and wetland birds in the marshes. Raccoons also forage in these areas.

Open water wetlands have been maintained through active and intensive management. Emergents within impoundments are managed to maintain a hemi-marsh condition. Tools such as burning, mowing, disking, and using herbicides have been used to reduce extensive stands of emergents. Occasional drawdowns oxidize nutrients and consolidate substrates to facilitate the germination of submergent vegetation, such as sago pondweed. When pond bottoms are exposed production of smartweed and other desirable native colonizers is higher after reflooding, especially in mudflats in shallow benches. Periodic drawdowns are occasionally used to remove invasive carp from impoundments. When impoundments cannot be totally dried up, rotenone, netting, and electroshocking have been used to remove invasive carp.