Contaminants in the Klamath Basin: Historical Patterns, Current Distribution, and Data Gap Identification

The Klamath Basin in California and Oregon is a diverse and productive region that supports numerous ecological, economic, and cultural benefits. However, competing uses and major changes to the Basin’s hydrology have severely impacted the natural resources of the region. Efforts are underway for major restoration activities within the basin, with the goal of better balancing the diverse use of land and water resources. However, the myriad of ecological stressors on the basin’s resources can complicate predicting the trajectory and success of restoration efforts, thus it is important to inventory those stressors and identify critical data gaps prior to implementing actions. The Klamath Basin (approximately 31,000 square kilometers) has a relatively well‐documented history of contaminant impacts associated with historical pesticide use on agricultural lands. Agriculture accounts for approximately 6 percent of the land use in the entire basin, most of which exists in the Lost River, Shasta River, and Upper Klamath Lake subbasins (59, 14, and 11 percent, respectively). However, a current inventory of available data on contaminant distribution and sources is lacking. Thus, the goal of this document is to summarize what is currently known about past and current contaminant distribution and impacts of contaminants on the ecological communities throughout the basin. Additionally, we identify key data gaps which, when addressed, will facilitate a more thorough understanding of the factors driving contaminant cycling and ecological exposure so that efforts can be implemented to help minimize the threats.