The effectiveness of an urban detention system, composed of a detention pond and wetlands in series, in reducing constituent loads carried in runoff was determined. The detention pond was effective in reducing loads of suspended solids and suspended metals. Suspended-phase efficiencies for solids, lead, and zinc ranged between 42 and 66%. Nutrient efficiencies were variable, ranging for all species and phases, from less than 0 to 72%. The wetlands generally was effective in reducing both suspended and dissolved loads of solids and metals. Total (dissolved + suspended) solids, lead, and zinc efficiencies ranged between 41 and 73%. Efficiencies for total nitrogen and phosphorus were 21 and 17%, respectively. The system, by combining the treatment of the pond of wetlands, was very effective in reducing loads of most constituents. Total solids, lead, and zinc efficiencies ranged between 55 and 83%. Total nitrogen and phosphorus efficiencies were 36 and 43%, respectively.The effectiveness of an urban detention system, composed of a detention pond and wetlands in series, in reducing constituent loads carried in runoff was determined. The detention pond was effective in reducing loads of suspended solids and suspended metals. Nutrient efficiencies were variable, ranging for all species and phases, from less than 0 to 72 percent. The wetlands generally was effective in reducing both suspended and dissolved loads of solids and metals. The system, by combining the treatment of the pond and wetlands, was very effective in reducing loads of most constituents.