Water-resources data for Colorado for the 1998 water year consist of records of stage, discharge, and water quality of streams; stage, contents, and water quality of lakes and reservoirs; and water levels and water quality of wells and springs. This report (Volumes 1 and 2) contains discharge records for 316 gaging stations, stage and contents of 26 lakes and reservoirs, discharge measurements for 1 partial-record low-flow station and 1 miscellaneous site, peak-flow information for 29 crest-stage partial-record stations; water quality for 118 gaging stations and for 8 lakes and reservoirs, supplemental water quality for 192 gaged sites; water quality for 72 miscellaneous sites and 14 observation wells; water levels for 3 observation wells, and meteorological data for 25 sites. Seven pertinent stations operated by bordering States also are included in this report. The records were collected and computed by the Water Resources Division of the U.S. Geological Survey under the direction of W.F. Horak, District Chief. These data represent that part of the National Water Data System collected by the U.S. Geological Survey and cooperating State and Federal agencies.