During June 1995-April 1996, the phytoplankton at four sectors (Sea, Boughaz, Lake and Drains) was investigated. A total of 204 species, were identified comprising 91 diatoms, 50 green algae, 27 blue- green algae, 16 dinoflagellates, 17
Euglenophyceae, 2 silicoflagellates and one Rhodophyceae. Diatoms were the most important algae in the four sectors, followed by green algae in Sea, Boughaz and Lake sectors, but blue-green algae ranked the second in Drains sector and mainly represented by Microcystis aeruginosa. Skeletonema costatum was the leading species in Sea sector, while the genus Nitzschia was the main component of Boughaz population. Cyclotella meneghiniana was the major dominant form in Lake sector. The phytoplankton crop showed a remarkable increase as compared with the previous records and the study indicated high level of eutrophication in Lake sector Phytoplankton diversity varied widely, low diversities were related to stable community states, while higher diversities corresponded to non-steady state periods. Inverse relationship between equitability and total number of individuals was observed. Lake Edku is a shallow brackish water lake subject to huge inputs of terrigenous and anthropogenic nutrients from drains discharge, sewage and agricultural runoff. These nutritional conditions make the lake biologically productive. It is situated west of the Rosetta Nile branch between longitudes 30° 8' 30" and 30° 23' E and latitudes 31° 10' and 31° 18'N(Fig.1)with depth varies from 20
to 140 cm. The eastern part of the lake receives large quantities.