Abstract Implementation of the Federal Clean Water Act and Oregon Senate Bill 1010 is proceeding under two simultaneous processes in Oregon. The Oregon Department of Environmental Quality is responsible for developing Total Maximum Daily Load (TMDL) allocations for water-quality limited water bodies. The Oregon Department of Agriculture is striving to develop Management Area Plans to provide guidance for management of private agricultural lands to meet Clean Water Act objectives. Both processes seek input from local advisory committees comprised of landowners and other stakeholders, and technical review committees. Klamath Lake and Klamath River have been designated water quality impaired for several parameters including nutrients. Researchers have attempted to determine the extent of agriculture's contributions to nutrient enrichment of surface waters in the Upper Klamath Basin. Two United States Geological Survey (USGS) studies focused attention on drainage of agricultural lands adjacent to Klamath Lake as a significant source of nutrient loading in the lake. A preliminary draft report by the Klamath River TMDL committee identified the outlet for drainage waters from the Klamath Irrigation Project to the Klamath River at the Straits Drain as a point source for nutrient loading. Preparation of a final TMDL for this sub-watershed was tabled pending development of a TMDL for Klamath Lake and its tributaries. Insufficient data are available to determine the relative contributions of agricultural activities, natural background sources, and other potential sources of nutrient enrichment to establish numerical limits for nutrient loading from agricultural lands. From 1998 through 2000, the Klamath Experiment Station has investigated nutrient loading from drainage of agricultural lands adjacent to Klamath Lake, natural background sources including major springs and several artesian wells, and loading to the Klamath Irrigation Project from diversions out of Klamath Lake and Klamath River. Findings indicate contributions from agricultural lands adjacent to Klamath Lake have been overestimated, and the Klamath Irrigation Project is probably a net sink for nutrients diverted out of Klamath Lake and Klamath River. Data to support these assertions are presented. Introduction Most of the surface waters in the Klamath Basin are included in the Oregon department of Environmental Quality (DEQ) 303D list as water-quality limited. While the only criterion for listing of many streams is temperature, based on a preliminary standard of 64°F, Klamath Lake and Klamath River are listed for chlorophyll a, dissolved oxygen, un-ionized ammonia, and pH. The DEQ is working toward development of TMDL allocations for Klamath River and
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