Many hazardous substances and mixtures are immiscible with and more dense than water. When spillages or releases into waterbodies occur, the hazardous materials will disperse in a pattern controlled by physical properties of the material, flow and dispersion effects, and topography of the waterbody bed. Mapping (i.e., location and thickness determination) of the spilled substance is essential for prompt and economical removal to protect biota and ensure minimal contamination of water. Analysis of the reflection patterns of acoustic waves (ca. 200 kHz) beamed into the water from a boat is shown in this and in previous work to serve as an excellent mapping technique. When the project to map pollutants was initiated, no suitable commercial devices were available. A very effective, portable, battery-operated prototype system was constructed. The reflection data (intensity vs time) were displayed on an on-board dual-trace oscilloscope that had time-delay features. Subsequently, a suitable commercial system was test marketed and has been successfully used in the field to locate creosote in a waterbody.