Suspended sediment and particulate phosphorus (P) loads from the Susquehanna River, the largest tributary to the Chesapeake Bay, have been increasing due to the infilling of the Lower Susquehanna reservoirs and event-driven scour of sediment from behind the dams. A synthesis of sediment-water exchange data along the Bay salinity gradient confirmed that P likely remains associated with particles except under sulfate reducing conditions in the mid-Bay, where the formation of iron sulfides releases iron-bound phosphate to the water column. To estimate what fraction of scoured particulate P could become bioavailable through iron sulfide formation, P was extracted from reservoir sediment samples using a sulfide solution. Other extractions were used to quantify total P, inorganic P, and iron. Sulfide-extractable P ranged up to about 35% of total P. Findings showed that the reactivity of scoured particulate P would likely be limited and dependent on environmental conditions at the site of deposition.