In 2018, a large, coordinated environmental flow was instituted along the Barwon-Darling (Barka) River to connect ecosystems and restore public confidence in water regulation in the Murray-Darling Basin. This article examines the multiple river realities enacted by this event—environmental flow, regulated flow, unregulated flow, shut-up flow—as a conflict over what constitutes the character of water during substantial change in Australia’s settler colonial systems of water governance. Geographical analyses of event spaces from military contexts assisted in unpacking the ontological and spatio-temporal matters germane to this situation in which managers needed to heed the dynamism of the river at both material and institutional registers. The article describes the scientific and regulatory practices and visual technologies through which management of an “event-ful” river brought together some waters (but not others) into something ontologically secure and coherent, and therefore governable. It shows how the naturalising discourse constrained and enabled what could be said about the relations deserving of water and who gets to decide what socio-material connections water might make. Aboriginal leaders interviewed during the flow chose to emphasise a wider relational set of connections than did state water managers, and to accentuate dysfunctional and destructive relations, thereby inviting others to think and feel differently about environmental flows.