The study looked at how different plants in wetlands can clean up sewage. They tested four wetlands with different plants and found that all of them helped remove nitrogen and phosphorus from the water. The wetlands with plants did better than the one without. Grassleaved Sweetflag was the most effective at cleaning up phosphorus. The plants absorb the pollutants as they grow, and microorganisms around their roots also help clean the water. Wetlands with plants are a good way to treat sewage with low levels of pollutants.