Two survey boats equipped with differential Global Positioning System (GPS) receivers and Turner Designs C3 submersible fluorometers were used to survey the spatial distribution of the Rhodamine WT dye in the Des Plaines River downstream of the Brandon Road Lock and Dam (BRLD) near Rockdale, Ilinois. Mapping of the dye plume commenced after the lock chamber at BRLD was dyed with 4 liters of Rhodamine WT dye during a routine filling procedure. Measurements of dye concentration downstream collected by these survey boats capture the leakage of dyed water from the lock, the pulse of dyed water exiting the lock during routine emptying of the lock, and the mixing of the dyed water downstream during a 17-minute flushing operation of the lock. The fluorometers were installed in a fixed, downlooking orientation approximately 1 foot below the water surface. Fluorometer readings were taken at a frequency of 1 measurement per second. Data were acquired on personal computers running Tera Term to log serial communication from the fluorometers. Raw (not georeferenced) data were stored internally on the fluorometers and downloaded following the survey. Survey techniques included streamwise transects through the dye plume in both the upstream and downstream direction, serpentine surveys, and near-bank surveys to capture the full spatial distribution. The boat survey crews also performed periodic, simultaneous discharge measurements at key locations in the approach channel to the BRLD and further downstream near the intakes and outfall of a power plant. Mooring of barges and active barge traffic restricted surveys in some locations and led to some contamination of fluorometer data by increasing local turbidity concentrations near the active vessels. These data have been screened out during processing. The C3 turbidity sensors were not calibrated and therefore reported only relative changes in background turbidity and not absolute turbidity values (in relative fluoroescence units (RFU)).