Donghu Lake> located at the northeastern part of Wuhan city, is a shallow lake with an area of 32 km². It is a hyper-eutrophic lake polluted by domestic sewage and industrial waste. The community structure, growth potential (AGP), cell density, chlorophylLa and primary production of algae in nine areas of the lake were investigated in 1991~1993. Green algae is the most important component and blue-green algae as well as diatoms are subdominant groups in the lake areas. The dense bloom of blue-green algae has vanished since 1985. The maximum AGP and primary production were found in Chagang area and the minimum in Niuchaohu area. According to the parameters concerning trophic level obtained in this study, the descending order of water quality of the nine lake areas is Niuchaohu area, Tanglinghu eirea, Houhu area, Guozhenghu area, Lingjiaohu area, Shaojihu area, Miaohu area, Yujiahu area and Chagang area. As compared with the algal data from Guozhenghu area (a typical sublake) after the 1950s, the decadal peak value of algal individuals increased over one hundred times in the past 40 years. However, the genera of algae in the sublake were reduced by 54% during the same period. The results clearly demonstrate that the eutrophication of Donghu Lake has not yet been controlled. The features of degenerated lake ecosystem are quite obvious in this lake.