Field studies were conducted in a Flowing Stream Test Facility to determine parameters governing application of floating media (in this case, commercially-available activated carbon) to flowing streams for the purpose of treating hazardous materials spills in situ. It was found that removal efficiency is highly dependent on prompt location of the contaminant plume, even dispersion of media over the water surface, and favorable environmental conditions. This technique is most effective for concentrated plumes in small streams, and removal efficiencies increase as the size of the spill increases. Removal efficiencies ranged from 50 to > 95%, depending upon the substance being used in the tests. Further investigation should focus on ballast and packaging techniques, methods for increasing efficiency of contact, prevention of carbon buildup along stream banks, and efficiency of spent carbon collection.