 Constructed wetlands will improve the runoff water quality depending on the wetland processes.The key treatment mechanism of wetlands are physical (trapping suspended solids and adsorbed pollutants), biological and chemical uptake (trapping dissolved pollutants, chemical adsorption of pollutants), and pollutant transformation (more stable sediment fixation, microbial processes, UV disinfection).The design of constructed wetlands requires careful consideration to avoid common problems such as accumulation of litter, oil and scum in sections of the wetland, infestation of weeds, mosquito problems or algal blooms.