Constructed wetlands provide good removals of BOD, COD, suspended solids, heavy metals, and pathogens from wastewaters being treated in them. However, although they are widely used in cold climates, winter operability often presents problems, and they normally only remove part of nitrogen and phosphorus nutrients in wastewaters being treated in them. What is needed was a new type of constructed wetland which removes nutrients as well as it does other contaminants, which operates better in cold weather, and which is able to handle especially difficult‐to‐treat wastewaters.