Water quality samples were collected in three sewer channels discharging into the Boeng Cheung Ek treatment wetland and at two longitudinal sites within the wetland (mid-point and outlet), principally during the dry season, but also during storm events. YSI datasondes were installed to collect data at 15-minute intervals for dissolved oxygen, turbidity, conductivity, temperature and pH, at two sites in the wetland. Levels of Cu, Cr, Zn, total phosphorus, nitrate, detergents, E. coli and total suspended solids entering Boeng Cheung Ek from the three main tributary sewer channels and levels in the outflow from the wetland were compared for the dry season. The difference in mean concentration between inlet and outlet reflected reductions in the range of 44% (nitrate) to 99.97% (E. coli), with other parameters fitting within this range. Load reductions also were calculated on a monthly basis. Several contaminants within the sewer channels were significantly diluted by stormwater during individual rain events, although this trend was not observed within the wetland. The YSI data exhibited both interesting daily trends for dissolved oxygen and dry season to rainy season trends in weekly mean values for dissolved oxygen and conductivity.