Acoustic velocity meters (AVM’s) and acoustic Doppler current profilers (ADCP’s) wereused to measure streamflow at four streamflow-gaging stations in the Chicago River system. Thestreamflow data were used to compute discharge and to determine the uncertainty in the computedannual mean discharge at each station for the Lake Michigan Diversion Project in Illinois.Descriptions of the instrumentation at each station, stage-area and index-velocity ratings, andmethods utilized for computing discharge and estimating missing record are given. Daily meanand annual mean discharges were computed for each station for 1997-99 water years (WY’s). Awater year is defined as the 12-month period from October 1 through September 30. The wateryear is designated by the calender year in which it ends and which includes 9 of the 12 months.Thus, the year ending September 30, 1999, is called the 1999 water year.