A Turner Designs C3 submersible fluorometer was deployed in the Brandon Road Lock chamber (BRLD) near Rockdale, Illinois, to measure Rhodamine WT dye concentrations during a U.S. Geological Survey dye study conducted on October 20, 2015. The lock chamber at BRLD was dyed with 4 liters of Rhodamine WT dye during a routine filling procedure. Measurements of dye concentration profiles were collected at 15 stations in the lock chamber and capture the three-dimensional distribution of the dye in the chamber after filling, after the lock was emptied, and after a 17-minute flushing operation of the lock. A series of five taglines and rope and pulley systems were used to position the fluorometer at each station to avoid putting a boat in the lock chamber and creating additional mixing. Fluorometer readings were taken at a frequency of 1 measurement every second.