Wyoming is one of a few states that allow the discharge of produced water from oil fields into surface waters for beneficial use by livestock and wildlife. Oil field discharges of produced water create wetlands that provide habitat for aquatic migratory birds and other wildlife. Wetlands surveyed in Wyoming from 1996 to 1999 showed that inefficient oil-water separation contributed to the discharge of oil into some wetlands receiving produced water. Over 62% of the sites surveyed had inadequate measures to exclude wildlife, particularly migratory birds, from entering skim pits used to separate oil from produced water. The risk of oil discharges into wetlands can be reduced significantly by proper maintenance of equipment used to separate oil from produced water; immediate removal of oil from production skim pits or tanks to prevent overflow into the receiving wetlands; installation of secondary or tertiary containment ponds or tanks to capture any oil accidentally discharged from the primary or secondary pits or tanks; or construction of wetland-based treatment systems for removing metals, radionuclides, and hydrocarbons from the produced water prior to discharge into natural wetlands. Wildlife mortality in skim pits can be prevented using closed containment systems, eliminating pits or keeping oil off open pits or ponds, or using effective and proven wildlife exclusionary devices.