Physical, chemical, and biological data were collected between 1990 and 1992 as part of a detailed study by the U.S. Department of the Interior of the effects of irrigation drainage on aquatic resources in the Klamath Basin of California and Oregon. Most of the sites for data collection were in and around the upper and lower sump of Tule Lake, in Tule Lake National Wildlife Refuge, and along major drains in Lower Klamath National Wildlife Refuge... In response to increasing concern about the effects of contaminated irrigation drainwater on human health, fish, and wildlife, the U.S. Department of the Interior established the Irrigation Water Quality Program to investigate irrigation-related water-quality problems at National Wildlife Refuges (NWR) and migratory bird use areas potentially affected by irrigation projects constructed or managed by the Department of the Interior. The Klamath Basin was one of the areas chosen for investigation