Water resources data for the 1974 water year for Iowa including records of streamflow or reservoir storage at gaging stations, partial-record stations, and miscellaneous sites, and records of water-quality data on the chemical and physical characteristics of surface and ground water, are given in this report. In Part 1, records are included for 127 gaging stations of which 119 are streamflow discharge stations, and 8 are reservoir or lake stations; also included are records for 426 low-flow partial-record stations, 128 crest-stage partial-record stations, and 30 miscellaneous sites. Locations of gaging stations are shown in Figure 2. In Part 2, water quality data on chemical, physical, biological, and sediment characteristics of surface water were collected from designated sampling sites at predetermined intervals such as once daily, weekly, monthly, or less frequently. Records are given for 353 sampling stations of which 23 are continuous record stations, 9 are partial-record stations, and 321 are miscellaneous sites. Locations of water-quality stations are shown in Figure 3. A summary of periodic water temperature data is given for 98 regular gaging stations. The records were collected and computed by the Water Resources Division of the U.S. Geological Survey under the direction of S.W. Wiitala, district chief. These data represent that portion of the National Water Data System collected by the U.S. Geological Survey and cooperating State and Federal agencies in Iowa.