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Stormwater wet ponds are ideal facilities for filter-based retrofits that enhance phosphorus (P) removal from pond outflow and thus reduce P loading to receiving waters. Sufficient land area to construct filters typically exists surrounding the pond. The elevation of the pond’s permanent pool and impoundment of runoff above the permanent pool during storm events should typically provide enough hydraulic head to operate gravity-flow filters. The primary impediments to enhanced P treatment at stormwater ponds are that P concentrations in outflows tend to be low and peak outflow rates are often high.