Abstract:In this study, phytoplankton abundance and community structure were investigated and analyzed from May 2007 to April 2008 in the Xionghe Reservoir, which is located in the Hubei Province of China. A total of 74 phytoplankton species, belonging to 49 genera were identified, consisting of 40 species of green algae, 15 species of blue-green algae, 11 species of diatoms, 3 species of dinoflagellates, 2 species of both golden algae and euglenoids, and only 1 species of cryptomonad. Blue-green algae peaked in July, dominant by Anabaena circinalis. Diatoms, the cryptomonad and dinoflagellates peaked in March, April, April, respectively. Dominant species of diatoms were Synedra amphicephala and Fragilaria pinnata, while that of the cryptomonad and dinoflagellates were Cryptomonas ovata and Peridinium bipes, respectively. The annual average values of diversity indices (D, H′), evenness (J) and abundance (Dm) of phytoplankton were 0.60, 2.20, 0.76, 1.15, respectively. The annual variations of diversity indices (D, H′) and evenness (J) of phytoplankton showed a clear seasonal pattern, but no clear spatial pattern.