Rock phosphate and other phosphorus fertilizers have been used previously to effectively fix bioavailable Pb in soil as extremely insoluble pyromorphite-like minerals. In this study, we immobilized rock phosphate in beads prepared from two different gel matrices, calcium alginate and agarose. These were put into mesh bags, placed at various locations in a stream that bisected the contaminated industrial site, and recovered every month over a three-month period of time. Total acid digestion of the phosphate beads indicated that they were effective in the detection of Pb being transported in stream water from the site, despite aqueous Pb concentrations in water that were below ICP-MS analysis detection limits. Calcium alginate-based beads disintegrated over time, suggesting the influence of a calcium-chelating agent in the stream water. The phosphate bead approach may facilitate the long-term monitoring of Pb remediation effectiveness at similar contaminated sites.