Abstract: This paper studied the phytoplankton and flow velocities of Suzhou Creek from December,2005 to July,2006 and discussed the correlation between them. The results showed that, in high-flow period, the quantity variations of Cyclotella sp.and Chlorella vulgaris were similar in different flow velocities. Cyclotella sp. and Chlorella vulgaris were both main dominant species of phytoplankton. And there were large variation in the quantity, species and the content of chlorophyll a of phytoplankton in different hydrographic periods.The quantity and species of algae were higher and more in high-flow period than that in low-flow period and average-flow period.During the three periods, the average content of chlorophyll a in neap tide was more than that in spring tide.

Key words: flow velocity, tide, phytoplankton, chlorophyll a, Suzhou Creek, hydrographic period, flow velocity, tide, phytoplankton, chlorophyll a, Suzhou Creek