Improving water quality through the use of floating macrophyte species is another phytotechnology application. For example, different types of duck weed and water hyacinths have been used as an alternative to waste stabilization ponds. The inorganic nitrogen and phosphorus contained in wastewater and decompos ed from organic pollutants by microorganisms are absorbed by the water hyacinths. The water hyacinths with microorganisms and organic materials attached or coagulated on root surfaces can then be harvested as feed for fish culture ponds and animal farms. However, use of water hyacinths requires strict control, as they can easily spread becoming a nuisance and also because they tend to incorporate and store heavy metals.