Phytoplankton structure and abundance were studied weekly in Boughaz El-Maadiya, a channel connecting between Lake Edku and the Mediterranean Sea at Abu Kir Bay. The study extended from the end of April to end of October 1997 at four locations representing different ecological conditions,Weekly changes were observed in both the structure and standing crop of phytoplankton due to changes of current direction towards the Lake or the Sea. The Majority of the recorded species were fresh or brackish water forms, while 39 species were marine. Diatoms were the most diversified group (77 spp.), followed by green algae (46 spp.), blue greens (30 spp.), Euglenophyceae (16 spp.) and dinoflagellates (13 spp.). The standing crop showed abnormal wide weekly variations between lOxlO3 and 36.8xl06 units l"1 for numerical density and 10.6-124.7 \x% I"1 for chlorophyll a Diatoms occupied the first order of abundance, constituting 54.5-81.6 % at different locations and then green algae (16.3-41.8 %). Both groups displayed obvious weekly variations, while other groups showed intermittent flash appearance with markedly lower densities. The species diversity as well as species richness were high,indicating spatial and temporal variations. Cluster analysis demonstrated three main groups of species that differed in their frequencies and abundance. The correlations between phytoplankton abundance and ecological parameters were oftenly insignificant reflecting strong role of the current regime on the phytoplankton distribution in Boughaz El-Maadiya.