The treatment performance of four horizontal and two up-flow pilot-scale constructed wetlands planted with Schoenoplectus validus were investigated over a 20 month period (two winters and two summers) treating dairy parlour wastewaters at a range of loading rates. Removal of BOD.TN and TP were positively correlated with retention time. Reduction of BOD (70 - 90%) and SS (40 - 90%) in relation to loading rate were similar in both flow formats. The horizontal-flow wetlands showed 40 - 90 % reduction of TN and 30 - 80 % reduction of TP. The up-flow wetlands showed reduced levels of TN and TP removal, particularly when the loading rates were increased during the latter 5 months of the trial. Results are compared with those of other published studies of horizontal and upflow wetlands treating NH4-N rich organic wastewaters.