The irrigated cotton industry in Australia has been developed around major river systems to allow water to be pumped to farm storages and then recirculated on farm using flood irrigation techniques. Recent work conducted by the Department of Water Resources NSW, showed that levels of some pesticides, particularly endosulfan, exceeded ANZECC guidelines for the protection of aquatic ecosystems in river systems in northern NSW. Because of the close proximity of natural water courses to cotton paddocks, a major national research programme was established in 1993, jointly funded by the Land & Water Resources Research and Development Corporation (L WRRDC), the Cotton Research & Development Corporation (CRDC) and the Murray Darling Basin Commission (MDBC). An important part of this program has been a project designed to estimate the contribution that the aerial application of pesticides (specifically endosulfan), makes to chemical loads in the riverine environment by primary droplet transmission (drift), subsequent volatilisation and transmission on dust particles.