Technical Abstract: High phosphorus (P) concentrations in drainage from agricultural lands that flows to the Chesapeake Bay contribute to impairment of water quality. Byproducts that effectively sorb P have been applied to soils and animal manure to reduce dissolved P losses in runoff from agricultural soils. Such materials have been directly applied to surface waters to reduce bioavailable P and protect against eutrophication. However, the long-term effectiveness of such treatment is unknown due to the fact that total P loads are unchanged. A filtration box filled with P sorbing byproducts was designed as a more permanent means of reducing P loads to surface waters by allowing P to be removed from the drainage basin. Byproducts were characterized and screened for potential use in a filtration box based on pH, buffer capacity, P sorption capacity, P retention capacity, heavy metal content, and chemical forms and concentrations of iron, aluminum, calcium, and magnesium. The byproduct selected for use in this particular study is derived from a passive system for treating low flow acid mine drainage sites. It contains high amounts of silt-sized iron and aluminum oxides and hydroxides and calcium carbonates and sulfates that may also be effective in reducing heavy metal concentrations in addition to P. The filtration box was designed based on target P removal, ditch flow rates, P loads, hydraulic head/available space, and hydraulic conductivity, P sorption kinetics, and P sorption capacity of the byproduct. The filtration box allows for flow bypass during large flow events and also provides easy access for removing/replacing P saturated byproduct. An agricultural drainage ditch located on the University of Maryland Eastern Shore research farm was selected for treatment. Inflow and outflow water quality data are presented as an assessment of the effectiveness of the filtration box for reducing P loads and heavy metal concentrations in drainage ditch water.