Marsh, swamps, or wetlands that have been created by people are considered to be constructed wetlands. They can be brand new or they are sometimes restored habitats that have been designed for the continuance of native and migratory wildlife or for the anthropogenic discharge of storm water and waste water. Often it is used as reclamation of land after ecological disturbances like in mining or refinery industries. It is used as a way to reclaim land after wetlands have been lost to developments. These constructed wetlands act as a biofilter by removing pollutants like heavy metals and sediments from the water by imitating the features of natural wetlands.
Surface flow reed beds are one of the characteristics of constructed wetlands. They have a horizontal flow of wastewater across the roots but are not used as often as they once were because it takes a large amount of land to purify the water and it is not as effective for purification in the winter. Instead subsurface flow reed beds are sometimes used. This is when the flow of wastewater happens between the roots of plants instead of at the water surface. This tends to be more efficient and has less of an odor and it is easier to maintain in the winter. Unfortunately, they do tend to clog more easily. Vertical flow reed beds have the same advantages is subsurface flow reed beds, but they use a pump to divide water at the bottom and find sand to increase the bacteria counts. The pumping is pulsed, which solves the clogging problem.