AbstractExtensive recording of currents, collection of water samples and routine meteorological and tide records provide a base for this study of the dynamics of Australia's largest river, the Murray, during one of its rare floods in 1974. The results suggest that the Coorong. a narrow lagoon extending from the river mouth to the Southeast, at right angles to prevailing winds, was formed as a flood escape mechanism. Geological evidence displays the existence of similar geometries formed in the past in an area which at one time was a deep gulf of the Southern Ocean extending into Australia. The same mechanism may have been at work elsewhere in the world.