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The Upper Snake-Rock (USR) watershed is one of eight special emphasis watersheds in the NRCS Conservation Effects Assessment Project (CEAP). Land use in the USR is 37% irrigated agriculture, <1% dryland agriculture, and 60% rangeland and forest with a history of various conservation practices and long-term water quality data. The project is focused on the Twin Falls irrigation district, which covers 82,000 ha of irrigated agriculture. The main conservation practice affecting water quality is conversion from furrow irrigation to sprinkler irrigation; however, other conservation practices implemented in the watershed include reduced tillage, sediment basins, and application of polyacrylamide in irrigation water. Watershed-scale water quality research in irrigated regions of the arid west must consider the elaborate canal and drainage systems that modify hydrology. Furthermore, in arid regions, the volume of surface runoff from scheduled irrigation events is much greater than from natural runoff. The objectives of this study are to i) determine the effects of conversion from furrow irrigation to sprinkler irrigation on surface water quality and quantity at the watershed scale and ii) determine the salt balance for the Twin Falls irrigation district. Water quality will be monitored within watershed sub-basins and related to cropping practices through the use of historical data and computer simulation models. Preliminary data suggest that sprinkler irrigation results in lower TSS and P concentrations in irrigation return flow than does furrow irrigation. Additional data must be collected prior to thorough data analysis.