Seasonal, local and monthly vertical variations in chlorophyll a concentration and in qualitative and quantitative counts in Aswan High Dam Lake (AHDL) phytoplankton were followed from March 1982 to February 1984. The chlorophyll a values correlated more or less with the total phytoplankton counts. Total algal counts exhibited considerable local variations in the different seasons and tended t o decrease in the most southern part of AHDL, especially during the flood period. The temporal course of algal development showed a n almost inverse trend to that of dissolved nitrate-nitrogen. The possibility of nitrogen limitation of algal growth was verified.Diatoms and blue-green algae alternated in the dominance of the phytoplankton community. The genera Cydotella and Anabaenopsis respectively were the most predominant genera among the diatoms and blue-greens and consequently in the phytoplankton community.

Variations in chlorophyll a concentration and in qualitative and quantitative counts of Nile phytoplankton were followed a t Assiut from September 1980 to September 1982. Chlorophyll a concentrations usually correlated well with phytoplankton density. The total phytoplankton exhibited higher counts in spring and summer than in autumn and winter. While diatoms exhibited the highest counts, green algae contributed more genera to the phytoplankton community.

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Monthly variations of some physical and chemical characteristics of Sile waters at Assiut (373 km south from Cairo, Egypt) during the period from September 1980 to September 1982 were followed and discudsed. As expected, the maximum temperature was recorded in summer and the minimum in winter. The pH values of Xile waters were recorded to be in the vicinit,y of 8.0. The highest, oxygen concentrations were recorded in the summer mont,hs, mainly due to the relatively high photosynthetic activity. The total soluble salts and the t,otal alkalinity exhibited almost identical t.rends. Nitrate, phosphate, silicate and chloride concentrations showed no major regular trends. The cation abundances by weight were as follows: Ca?+ > S a + zMgZ+>K+.

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