The US Department of Energy's Hanford Site, by virtue of its large size of 1,450 km2 (560 mi2) and conservative use of undeveloped land, provides a sanctuary for plant and animal populations that have been eliminated from, or greatly reduced on, surrounding areas primarily as a result of decades of intensive agriculture. This paper describes Hanford Site biota with emphasis on fishes and other animal wildlife that are currently surveyed as part of a continuing environmental monitoring programme.