The technology for using artificial marsh systems for upgrading domestic sewage effluent from primary settling tanks and/or facultative or aerated lagoons has been sufficiently developed to meet secondary and advanced secondary levels of treatment in the Southern U.S. Artificial marshes using emergent plants such as the bulrush combined with duckweed are also developed to the level of being a promising alternative wastewater treatment system for temperate areas throughout most of the U.S. Three types of artificial marsh wastewater treatment systems are either being installed or are under consideration for use throughout the Southern U.S. One system includes a shallow channel with a wastewater depth of 30 cm or less with rooted Southern bulrush (Scirpus californicus) and in some systems, floating duckweed. This system requires a hydraulic retention time of 5-8 days and can function with narrow, long channels. The shallow depth is important to achieve aerobic conditions before effluent discharge. A second type system includes a combination rock-plant filter and requires a reduced hydraulic retention time of 12-48 hours. The rock sizes and filter width-to-length ratio is important because of hydraulic back-pressure created when large volumes of wastewater flow through small rock filters. When large rocks are used, the back-pressure and filter pooling is eliminated, but longer plant growth periods are required for the plant roots to fill the large void area within the rock filter. Optimum wastewater treatment levels may take up to two years to develop when rocks greater than 10 cm are used. The third and most effective artificial marsh wastewater treatment system includes a combination of open channel rooted plant filters followed by rock-plant filters and can be used for treating a wide variety of wastewater. The retention times can be reduced in both when used in series.