Solubilization and transport of phosphorus (P) to the water environment is a critical environmental issue. Flocs resulting from neutralizing acid mine drainage (AMD) were tested as a possible low-cost amendment to reduce the loss of soluble P from agricultural fields and animal wastewater. Flocs were prepared by neutralizing natural and synthetic solutions of AMD with limestone, lime, ammonium hydroxide, and sodium hydroxide. Phosphorus sequestration was tested in three distinct environments: water, soil, and manure storage basins. In water, flocs prepared from AMD adsorbed 10 to 20 g P kg⁻¹ dry floc in equilibrium with 1 mg L⁻¹ soluble P. Similar results were observed for both Fe-based and Al-based synthetic flocs. A local soil sample adsorbed about 0.1 g P kg⁻¹, about two orders of magnitude less. The AMD-derived flocs were mixed with a high-P soil at 5 to 80 g floc kg⁻¹ soil, followed by water and acid (Mehlich-1) extractions. All flocs performed similarly. About 70% of the water-extractable P was sequestered by the floc when applied at a rate of 20 g floc kg⁻¹ soil, whereas plant-available P only decreased by about 30%. Under anaerobic conditions simulating manure storage basins, all AMD flocs reduced soluble P by greater than 95% at a rate of 0.2 g floc g⁻¹ rainbow trout (Oncorhynchus mykiss) manure. These findings indicate that AMD flocs could be an effective agent for preventing soluble P losses from soil and manure to the water environment, while at the same time decreasing the costs associated with AMD treatment.