When there are excessive floating plants, such as common water hyacinth or water cabbage, it means there are too many nutrients in the water. This may be caused by the discharge of fertilizers, livestock wastewater or municipal effluent. When there is heavy rainfall, the water cannot flow out. This phenomenon is called “eutrophication”. Fish living in eutrophic water are mostly strong species, such as tilapia and suckermouth catfish, and there is little biodiversity in the water.