Wetlands can be found near water bodies in urban areas such as the sea, estuaries/tidal rivers, reservoirs, ponds, canals, lakes, rivers/streams, and constructed wetlands. In cities, they can lower costs of water treatment, reduce flood risks and decrease a need for large grey infrastructure that stores or directs stormwater. Wetlands consist of various vegetation, soil, and microbial populations.

They carry many natural functions. Wetlands can be used to treat contaminants in surface water and groundwater or to purify waste streams. Also, wetlands are very rich in biodiversity by producing great volumes of food and sustaining many species.