The researchers studied the phytoplankton in Dalian Lake, Shanghai, to understand its community structure and water quality. They found 64 species of phytoplankton, with Chlorophyta being the most common. The density of phytoplankton varied throughout the year, indicating the lake is between mesotrophication and eutrophication. The Pielou evenness index was found to be a suitable indicator of the lake's eutrophication state, while the Shannon-Wiener diversity index and Margalef richness index were not as accurate.