The detention basin can be used to control the flood, protect the ecology and offer spaces for people to relax in the city. In order to avoid bad smell and mosquitoes in summer, the modular floating islands are designed to decrease water pollution and Eutrophication as well as achieve water purification. By the principle of minimizing the impact of flood retention and optimize the city environmental image, the design focuses on combining leisure activities, education and environmental function at the same time. It can also facilitate the further purpose for public uses.