This article analyses research that has explored the potential of a focus on indeterminate bodies for decision making, policy and politics. Drawing on different ways of conceptualising indeterminacy in scientific and policy domains it describes the Loweswater Care Project, a participatory ‘knowledge collective’ that attempted to avoid converting the complexities of vital cyanobacterial bodies into a purely social or managerial set of questions around water quality. Through a commitment to opening out the nature of ‘things’, participants in this collective honed new questions and avenues of inquiry around cyanobacteria and its relations. The Loweswater Care Project was a kind of ‘open’ in Haraway’s sense, where questions and demands are put to bodies, and to the apparatus that allows us to sense them, in ways that do not shy away from the probabilistic character of entities and their relations. The implications of generating indeterminacies in this setting are explored for environmental decision making, policy and politics.