The study looked at how clogging affects the flow and efficiency of wastewater treatment in constructed wetlands. They used a tracer to track water flow in wetlands with and without plants. Before clogging, plants shortened the time water stayed in the wetlands. After clogging, the effect was different in different types of wetlands. Clogging increased the time water stayed in the wetlands, improving purification but reducing treatment capacity. In some cases, severe clogging could stop treatment altogether.