Floating wetlands are used to reduce the growth of algae that causing to Eutrophication (excessive growth of algae becasue the water becomes overly enriched with minerals & nutrients). In Colombo (our main city) there's a lake called Bere lake , that suffer from eutrophication. So I decided to make 10 floating wetlands with some of my scout mates to reduce the growth of algae in Bere lake. Simpally Floating Wetlands are plant beds that are floating. The wetland managaement division of Sri Lanka Land Development Cooperation (SLLDC)  invented this concept to Sri Lanka & they supported & instructed us to do this successfully. We built 9 Floating Wetlands & planted 90 plants  on these units.