Effluents from both cells of a two-cell anaerobic lagoon system beating flushed swine waste were loaded into two types of constructed wetlands [submerged flow (SF) and free water surface (FWS)]. The wetlands were planted to Scirpus lacustris (Bulrush), Juncus Effusus (Soft Rush), and Saggitaria latifolia (Arrowhead). Passing anaerobic lagoon effluents through the constructed wetlands resulted in the following average reductions in water quality parameters: BOD5, 18 to 50%; NH3-N, 17 to 41%; TSS, 34 to 48%; total phosphorus, 15 to 30%. Effluents from the lagoons were too concentrated to achieve wetland effluent criteria suggested by the Natural Resource Conservation Service. This study showed that the Rational Method for sizing constructed wetlands to treat anaerobic swine lagoon wastewaters to achieve a wetland effluent criteria <30 mg/L BOD5 was inadequate. Continuous reduced environmental conditions in the wetlands was the primary reason for this, but high ammonia and TKN loadings also contributed.