Residues of 2,3,6-trichloro-phenylacetic acid (fenac) and 2,6-dichlorobenzonitrile (dichlobenil) were determined in irrigation water flowing over canal-bottom plots treated with the herbicides prior to the entry of water. Concentrations of fenac and dichlobenil in the first water to flow over the entire treated plots were 8.82 and 8.63 ppm, respectively. The bulk of the residues was transported from the plots in a very short time, and safe levels were reached after 1 hr. of water flow. The dichlobenil burden, picked up by water as it flowed over the treated plot, was effectively reduced as the water passed over untreated canal soil downstream.