This paper examines two interrelated cases of environmental injustice and social mobilisation in the Onondaga lake watershed in Central New York State, USA: (1) the case of the Onondaga Nation, an indigenous people whose rights to, and uses of, water and other resources have been severely reduced through historical processes of Euro-American settlement and industrial development; and (2) the case of the city of Syracuse, New York’s Southside neighbourhood, a low-income community of colour, where a sewage treatment facility was constructed as part of a broader effort to remediate the effects of pollution in Onondaga lake. The Onondaga Nation and the Southside neighbourhood are connected by Onondaga creek, which flows through each before joining Onondaga lake. These communities are also linked by shared histories of marginalisation and environmental injustice. Taken together, the cases demonstrate the temporal and spatial continuities of social relations of power, and their embodiment in water resources. Conceptually, the paper brings together the literatures of environmental justice and the political ecology of water resources. In doing so, we employ the concept of waterscape as an analytical lens to examine processes of marginalisation and social exclusion in the Onondaga lake watershed. The waterscape concept, and the political ecology of water resources literature more generally, have much to contribute to the study of water-related environmental (in)justice