Grays Lake NWR is in a high mountain valley, with probably the largest hardstem bulrush marsh in North America. This marsh is surrounded by tall grass wet meadows. Grays Lake supports the world?s largest breeding population of Greater Sandhill Cranes. Small components of surrounding habitat include tall wet meadow, aspen, willow, and mountain brush.
Waterfowl and waterbirds are the primary avifauna at Grays Lake. Because the marsh supports almost no fish, piscivorous waterbirds are absent. Tall grass wet meadows around the marsh support Bobolinks, and Savannah Sparrows, while the willow patches support Willow Flycatchers and Yellow Warblers. There is a hack tower on the refuge that is used annually by nesting Peregrine Falcons.
Largest breeding concentration of Sandhill Cranes* (250 pairs) in the world. Numerous waterfowl species nest here, including Trumpeter Swans, as well as shorebirds (Killdeer, Long-billed Curlew, Willet, Spotted Sandpiper, Willet, Wilson?s phalarope, Wilson?s Snipe), waterbirds (American Coot, Virginia Rail, Sora, American Bittern; plus colonial species listed below), and Northern Harriers. During migration, shorebirds (Greater Yellowlegs, American Avocet, Sandpipers) are abundant.
Colonies: Eared Grebe (15-20 nests), White-faced Ibis (up to 2,000 birds), Franklin?s Gull (up to 40,000 birds), Black Tern, Forster?s Tern
Introduced noxious weeds are a problem at this site, which could become more serious, and are being treated with chemical, mechanical, and biological control measures. The Fort Hall Irrigation District could drain more water from the marsh or drain it earlier in the year, so refuge managers are working with the District to improve water regime for wildlife. In recent years, drought has become a significant problem, and may be resulting in the observed decrease in size of the White-faced Ibis and Franklin's Gull colony. Renewed gold mining on Caribou Mountain could lead to increased sedimentation on the refuge. Because neighboring properties are owned by various private landowners and groups, the refuge strives to buy land as it comes available.
The majority of the area is hardstem bulrush marsh. There are large tall grass wet meadows around the marsh. Other habitats include croplands, willow, aspen, and mountain brush (these are minor components compared to marsh and grassland). The natural drainage is to Willow Creek to the North. A new outlet was dug at the southern end, draining into Blackfoot Reservoir and the Fort Hall Irrigation System. Fort Hall Irrigation District owns the water in the marsh and water levels are managed by agreement among the Irrigation District, the Refuge, and landowners.