This paper summarises the hydrological activities undertaken from May 1989 to January 1990 to investigate the effectiveness of a deliberate trial lowering and refilling of Lake Bonney (Barmera) South Australia, in an effort to reduce lake water salinity. A brief comparison with an earlier trial in 1973 and with a further water level manipulation in July 1990 is also made. In addition to an outline of the methodology and the technical results the social, political, economic and environmental implications are discussed.