The Lahontan Valley Wetlands are a remnant of ancient Lake Lahontan, a Pleistocene lake that once covered 8,665 square miles of western and northern Nevada. That lake reached its maximum extent about 14,000 years ago, then receded in stages as the climate in western North America entered an extended period of declining precipitation. The Lahontan Valley Wetlands began to emerge from the lake bed about 10,000 years ago (Chisholm & Neel 2002). Today the wetlands form the most important waterfowl breeding and migratory site in Nevada and are critical to many species using the Pacific Flyway.

Depending on water levels, the area is visited by up to 250,000 shorebirds, including Long-billed Dowitcher, Western and Least sandpipers, American Avocet, Wilson's Phalarope, and Long-billed Curlew, with peak numbers in the latter part of April, and again on the latter part of August. Nearly a quarter of a million coots have been recorded in the fall. Migration also brings thousands of waterfowl, including Snow Goose and smaller numbers of Ross' and White-fronted geese, along with Gadwall, Northern Pintail, and Green-winged and Cinnamon Teal; the wetlands are particularly critical for Canvasback, with up to 28,000 recorded, and Redhead, with up to 29,000 recorded during migration. The area just upstream from the terminus of the Carson River acts as a migrant trap, particularly during the fall, and large numbers of raptors use the wetlands during the winter. The wetlands are also important during the breeding season. With up to 10,000 birds, Stillwater National Wildlife Refuge has the world's largest colony of White-faced Ibis. Up to 5,000 American Avocet remain to breed, as do close to 700 Snowy Plover. (Chipley et al. 2003).

System is chronically threatened by invasive species, including cheat grass, tall whitetop, salt cedar (tamarisk), and Russian olive. Chronic water shortages plague wetlands because of agricultural diversions and over-appropriation of water in the Carson River system. Increasing off-road vehicle use. Predators exerting a strong influence on the success of waterfowl and shorebird breeding.