Excess riverine phosphorus is a worldwide threat to water quality. Leveraging 51 394 phosphate (PO₄³⁻) and 285 675 total phosphorus (TP) data points and hydrological topology information, we developed a new dataset mapping PO₄³⁻ and TP gain/loss across catchments in the conterminous United States. The new net phosphorus gain/loss maps allow us to assess sources, drivers, and model fidelity, thereby supporting future research and management of phosphorus contamination.