The concept of waste pervades contemporary water policy and the polarised debates about river management in Australia’s Murray-Darling Basin. However, the preoccupation with waste, and its associated notions of efficiency and productivity, is not merely a reaction to the relatively recent environmental critique prompted by excessive extraction from rivers and streams. We argue that the fixation with eradicating waste is embedded in the Australian colonial political imagination, where it has served as a powerful catalyst for projects of river transformation and as justification for territorial control of water. Initially control was exerted by Australian colonies and then later by state governments. A close examination of South Australia’s portion of the River Murray between 1880 and 1940 identifies four sites that were perceived as wasteful: the ocean to which the River Murray runs, wetlands, lakes and the atmosphere. To eliminate waste from and above the land surface, hydro-engineers and settler authorities transformed the lower River Murray with weirs, locks and barrages, at the same time as they altered society–water relations. Waste was articulated and acted on from within colonial processes with such force that the effects continue to set the parameters for today’s water policies and wider settler societal relations with rivers.