This site comprises two separate units that function together as a single system. The Toppenish Creek unit consists of the Toppenish Creek floodplain between Island Road and Slayton Road, six kilometers south of the town of Toppenish, and a 650-hectare patch of shrubbe-steppe between Pumphouse Road and State Route 97 on the north face of Toppenish Ridge. The Yakima Oxbows unit includes the mouth of Toppenish Creek and the Yakima River floodplain between the towns of Granger and Mabton. This IBA includes Toppenish National Wildlife Refuge and the Sunnyside State Wildlife Area. Public access is restricted in most of the area.
The floodplains of this site are rich in natural wetlands, channels, sloughs, and oxbow lakes, providing prime habitat for aquatic birds and raptors. The wetland habitat on the refuge is enhanced by managed water levels in the wetlands. The IBA's primary importance is as a wintering area for waterfowl, and as a breeding area for herons and bitterns. Dominant species of waterfowl are Mallard, Northern Pintail, American Wigeon, and Green-winged Teal. Breeding shorebirds are predominantly Black-necked Stilt, Long-billed Curlew, and American Avocet. The riparian forests, grasslands, and shrub-steppe flanking the streams and wetlands provide rich foraging areas for birds of prey.