When Dursban® (O,O-diethyl O-3,5,6-trichloro-2-pyridyl phosphorothioatte) is applied to polluted water sources for mosquito control, it quickly becomes widely distributed throughout the body of water; during the first few days after treatment, adsorption onto organic solids causes of the insecticide to leave the water phase. In the of organic matter, Dursban has limited hydrolytic stability, which is temperature dependent. These qualities allow for use of this insecticide in polluted waters for effective and rather long-term control of mosquito larvae. The high organic content of polluted water beds acts as a filter to remove the insecticide from the water. This characteristic, coupled with the limited hydrolytic stability of the compound, gives strong indications that insecticide pollution of sub-surface waters will not result.