Technical Abstract: The Upper Snake-Rock (USR) Conservation Effects Assessment Project (CEAP) was initiated in 2005 to determine the effectiveness of conservation practices in an irrigated watershed. Our objectives were to determine water and salt balances and water quality effects of using sprinkler rather than furrow irrigation in the Twin Falls irrigation tract in southern Idaho. Data from the current study were compared with earlier studies conducted from 1968 to 1971. Irrigation water diverted from the Snake River supplied 73% and 83% of the hydrologic input to this 82,000 ha (202,000 a) watershed in 2005 and 2006, respectively, with approximately 40% flowing back to the Snake River through furrow irrigation runoff, unused irrigation water, and subsurface drainage. Net suspended sediment loss decreased from 460 kg/ha (400 lb/a) during the 1971 irrigation season to 220 kg/ha (190 lb/a) in 2005 and 10 kg/ha (9 lb/a) in 2006 by switching from furrow to sprinkler irrigation, applying polyacylamide, and installing sediment ponds. The relative amount of sprinkler irrigation in a sub-watershed did not correlate with the total loss of suspended sediment for July 2005 and 2006 (r=0.12). The lack of correlation was primarily due to extremely high sediment concentrations in two of the five sub-watersheds, possibly due to furrow irrigation management. Two potential concerns identified during this initial analysis were an accumulation of total salts in the watershed and increased nitrate concentrations in four return flow streams compared to earlier studies. Future analyses will determine the effects of specific practices with this watershed.