This article examines the River Wye in the southwest UK as a political ecology marked by relations of colonial inheritance. A controversial case of contemporary British river pollution, the Wye is suffering from increasingly dramatic eutrophication events, with nutrient pollution from mineral phosphate fertilisers used in industrial agriculture causing algal blooms that destroy the river's ecology. This paper complicates dominant framings of the Wye's eutrophication as a local event and future crisis, instead arguing that eutrophication is structured by over a century of colonial histories of phosphate. Motivated by recent debates in geography and other cognate disciplines on decolonial ecology and the Plantationocene that point to the colonial origins of ecological crisis, this paper develops a theoretical framework of inheritance/transmission to articulate the situated histories of violence and dispossession shaping phosphate matter. It then empirically tracks the phosphate inheritances of the Wye by analysing the archives of the British Phosphate Commissioners (1873–1983), a 20th century governmental company that procured fertiliser for the British Empire by intensively mining phosphates on the Pacific Islands of Nauru and Banaba. Through this archive emerges a history in which, on a national and local level, the Wye is connected to the people, corporations, and institutions responsible for the emergence of the mineral phosphates industry that has spread ecological devastation across the globe. Through theoretically and empirically examining the Wye's phosphate inheritances, this paper foregrounds ethical obligations to think systematically and historically about phosphates as a prerequisite for bringing about deep structural changes needed to repair phosphate's harms.