- Deer Flat NWR consists of Lake Lowell and Snake River Islands sectors. The Lake Lowell sector is imposed on Bureau of Reclamation irrigation project reservoir in Boise River Valley, 4 miles southwest of Nampa, Idaho.
Lake Lowell is fed by water from the Boise River through the New York Canal, forming one of the largest off-stream impoundments in the West. Lake water is manipulated for irrigation with the refuge having no say in water management. Normal lake operation provides for the habitat needs of a wide variety of migratory birds.
The climate is arid to semiarid (about 9 inches of annual precipitation, mostly light snowfall and spring rain). Summers are dry, sunny, and warm; winters in the valley are cool and mild compared to the surrounding higher elevations. Refuge uplands are sagebrush/rabbitbrush/grass habitats; riparian zones are occupied by cottonwood, willow, and Russian olive. Spectacular concentrations of waterfowl occur on the Lake Lowell sector during peak migration.
The Snake River Islands sector encompasses 94 islands along 113 miles of the Snake River in southwestern Idaho and eastern Oregon. Objectives are to preserve and maintain habitat for all native species. The islands (<1 acre to 58 acres, 4-10 feet above mean river level) are especially important to nesting Canada geese of the southwest Idaho flock.
Upstream islands have grass/sagebrush centers and are ringed by willow and other riparian vegetation. Downstream islands are more heavily vegetated, with grassy centers bordered by larder trees such as willows, cottonwoods, and Russian olives.