Wastewater stabilization ponds are engineered ponds or lagoons that may be aerobic (mixed) or facultative (no mixing, but deeper) to allow settling and in-situ decomposition of wastes. Wastewater stabilization pond technologies are typically designed for centralized systems and can be used in a range of community sizes from small towns to large cities. These are low-tech systems most commonly used for treating blackwater and stormwater, removing suspended solids, treating organic waste, and providing passive reduction of nitrogen and phosphorus. Wastewater stabilization ponds are typically constructed to provide primary treatment and secondary treatment but can be constructed in a series or to include floating wetland islands to yield tertiary treatment water quality. They are simple to operate, with appropriate planning, and can be enlarged as communities grow. Advanced systems can be designed to enhance nitrogen and phosphorus removal.