The collection of hydrologic data and the investigation of the quantity, quality, and use of surface-and ground-water resources are major components of the mission of the Water Resources Division (WRD), U.S. Geological Survey (USGS). To accomplish this mission, the Arizona District is organized into a District office in Tucson and field offices in Tempe, Flagstaff, and Yuma, Arizona. These offices are geographically located in the State to provide access and response to hydrologic events and to maintain liaison with cooperating State and Federal agencies. The Arizona District technical staff is organized into two major sections: (1) the Hydrologic Data Section, which maintains the systematic hydrologic-data programs for the State, and (2) the Hydrologic Investigations and Research Section, which investigates and assesses the quantity, quality, and use of the State's water resources.The Hydrologic Data Section maintains a network of hydrologic data-collection sites and compiles hydrologic data collected from these sites for public distribution. These hydrologic data include records of (1) stage and discharge of principal rivers and tributaries; (2) chemistry and suspended-sediment concentration of selected rivers; (3) water levels and quality of the water in the principal aquifers; and (4) surface-and ground-water use. Data from this network are compiled and entered into the District data base and published annually in the report series "Water Resources Data Arizona." To provide a single point of retrieval for the public, data from this network also are compiled on the USGS World Wide Web server, located in Reston, Virginia (water.usgs.gov). The Hydrologic Data Section has made substantial progress in developing a real-time hydrologic data base. Surface-water data from selected sites are transmitted to the Arizona District's central hydrologic data base at regular intervals using satellite telemetry. This information is accessible to scientists or water managers to assess current hydrologic conditions. Real-time stream-discharge data for 121 streamflow-gaging stations are available at the Arizona District home page on the World Wide Web at http://wwwdaztcn.ivr.usgs.gov.The updated version of the National Water-Information System (NWIS) was installed in all WRD offices in 1997. This version is a Unix-based system that runs on the Data General platform. This release includes improvements for the National Water-Quality Assessment (NAWQA) study, programs to retrieve real-time data for display on the World Wide Web, and programs to facilitate management of real-time data. As this report was being compiled, the Arizona NWIS staff was working on another NWIS release scheduled for December 1997 that would include performance and technical improvements.The investigation and assessment of the surface-and ground-water resources of Arizona is accomplished through a series of projects conducted by the Hydrologic Investigations and Research Section. Each project is managed by a designated project chief who is responsible for ma...