This site is an irrigation reservoir with surrounding wetland habitat. The reservoir provides shallow feeding area for waterfowl and mudflats for migrating shorebirds. The site also contains some excellent bottomland cottonwood forests, mostly on Fort Hall Indian Reservation. The reservation also includes a large area of springs that support willow habitat.
Avifauna at American Falls Reservoir is among the most diverse in Idaho. There are over 200sp. recorded in area including many rare Idaho species. The reservoir attracts thousands of ducks, geese, and shorebirds. It is a breeding area for Trumpeter Swans, a staging area for Sandhill Cranes, as well as a wintering area for Bald Eagles.
*Intermountain West Regional Shorebird Plan names this as one of only 2 sites (other is Lake Lowell at Deer Flat NWR) in Idaho with greater than 5000 shorebirds in more than half years surveyed (Peak = 5,000-10,000). Species occurring regularly during migration include: Black-bellied plover, American Golden Plover, Snowy Plover, Killdeer, Black-necked Stilt, American Avocet, Greater Yellowlegs, Lesser Yellowlegs, Willet, Spotted Sandpiper, Marbled Godwit, Sanderling, Semipalmated Sandpiper, Western Sandpiper, Least Sandpiper, Baird?s Sandpiper, Pectoral Sandpiper, Dunlin, Long-billed Dowitcher, Wilson?s Snipe, and Red-necked phalarope.
Colonies: Eared Grebe (McTucker-Danielson), Western and Clark?s Grebe (McTucker-Danielson, Raibow &Seagull; 75-100 pairs), Double-crested Cormorant (McTucker-Danielson, Portneuf Mouth; 400-420 nests), Great Blue Heron (McTucker-Danielson; 30-50 nests), Black-crowned Night Heron (McTucker-Danielson; 70-90 nests), Snowy Egret (McTucker-Danielson, Portneuf Mouth), Great Egret (Portneuf Mouth), Cattle Egret (Portneuf Mouth), White-faced Ibis (McTucker-Danielson; 200-250 nests), Forster?s Tern (McTucker-Danielson), Black Tern (Portneuf Mouth), California Gull (Gull Island; 7000-8000 nests), Ring-billed Gull (Gull Island; 2000-2200 nests)
Nutrient enrichment and pesticide runoff from surrounding agriculture lands is a problem. Recreational activities are a disturbance to the avifauna and there have been several episodes of botulism in the waterfowl. In addition, grazing may reduce the understory in willow and cottonwood habitats as well as contributing to the introduction of nutrients in the form of wastes to the system. A management plan has been written for the reservoir, and an irrigation water operation plan by the U.S. Bureau of Reclamation is in progress. Because of the impressive numbers of shorebirds using this site, the Springfield Bottoms portion of the site has been designated as Idaho's only Western Hemisphere Shorebird Reserve Network (WHSRN) site.
Dominant habitat is shallow water aquatic. Other major habitats include riparian willow and bottomland cottonwood. Surrounding habitats are sagebrush or agricultural fields. There are several small towns adjacent to the reservoir. There are high sand bluffs supporting nesting Barn Owls and thousands of Bank and Northern Rough-winged Swallows.