Five Turner Designs C3 submersible fluorometers were deployed in the Des Plaines River downstream of the Brandon Road Lock and Dam (BRLD) near Rockdale, IL to measure Rhodamine WT dye concentrations during a U.S. Geological Survey dye study conducted on October 20-21, 2015. 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 instruments 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 on both sides of the approach channel to the lock at five fixed locations approximately 1.5 to 4 feet below the water surface depending on the location. Fluorometer readings were taken at a frequency of 1 measurement every 30 seconds. Mooring of barges and active barge traffic 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)).