The abundance and preferences of individual invertebrate populations (including zooplankton) closely associated with the substrates provided by aquatic plant structures and open-water areas of Lake Nasser were quantified in this study in order to gain understanding of the importance of submerged macrophyte for invertebrate diversity, and their relation to water properties. The following water parameters were measured: temperature, pH, dissolved oxygen (DO), total dissolved salts, electrical conductivity, turbidity, total suspended solids, carbonate, bicarbonate, nitrate, nitrite, phosphate, sulphate, silica, potassium, total hardness, calcium and magnesium.Five macrophyte species were recorded: Myriopyllum spicatum, Najas horrida, Potamogeton schweinfurthii, Potamogeton pectinatus and Vallisneria spiralis. In total 67 invertebrate species were recorded, comprising 39 Rotifera, 12 Cladocera, 4 Copepoda, 4 Insecta, 2 Protozoa, 2 Ostracoda and one species of Turbellaria, Tardigrada, Annelida and Nematoda. Thirty-seven species were exclusively epiphytic, 11 species were collectively planktonic and 19 species were found in both habitats. The greatest abundance of epiphytic invertebrates occurred in association with N. horrida-P. schweinfurthii community.The results indicated that total suspended solids (TSS), TH and NO 2 are the most influential water variables on the distribution of the aquatic macrophyte samples and their invertebrate communities. Also, the study indicates that water variables have a higher impact on the aquatic macrophytes than on the associated invertebrate populations. P, NO 3 , K, Na, Mg, Cl and DO were the most influential water variables that dictate the distribution of invertebrate groups recorded in the open-water zone. Water temperature, electric conductivity, pH, NO 2 , SO 4 ÀÀ , SiO 3 À , CO 3 ÀÀ and turbidity have a lesser influence of the distribution of the invertebrates recorded in this zone.

The objective of the study was to determine which factors regulate zooplankton organisms along Lake Nasser. Temperature, pH, DO, conductivity, turbidity, nutrients, and zooplankton abundance were measured. Twentythree species of zooplankton were recorded in Lake Nasser included in Copepoda, Cladocera and Rotifera. Copepoda represented the main bulk of the community. The lowest standing stock of zooplankton was noticed during spring due to the highest fish predation during this season associated with the lowest turbidity. Big difference in temperature in Lake Nasser along the year round is considered as a controlling factor related to range of tolerance of species. The oscillation of the lake water level and the different factors affect the standing stock of zooplankton in the lake. Thus, continuous monitoring of Lake Nasser biota should be undertaken to follow the changes in the ecosystem.

he morophometric configuration of lakes or reservoirs plays an important role in their water quality variations. The morophometry of Lake Nasser is characterized by the presence of many dendritic side extensions known as side channels or Khors. The surface area, depth and shape of these Khors depend upon the water level upstream the Aswan High Dam (AHD). In the last decade, the water level upstream the Dam fluctuated from about 181m ASL during year 2001 to about 174 m ASL during year 2005.This Fluctuation of water level from year to year affects water quality status of the Lake and its Khors due to the change of their morophometric configuration. To study the effect of water level fluctuation, four main important Khors characterized by gentle slope and sandy bottom with different size were selected. These Khors are Kalabsha, El-Alaki, Toushka, and Sara at Km, 41, 91, 247, and 325 from AHD respectively. The main goal for the present study is to assess the quality of water in the main Khors of Lake Nasser and its main channel during periods of low and high water levels (years 2001 and 2005 respectively). This assessment explores the potential pollution hazards coming from these Khors to the whole Lake. To achieve this goal water quality data generated from the analysis of water samples collected from the Khors and main channel during high and low water levels were used to calculate the water quality and trophic state indices as well as determination of the limiting nutrient factor of the lake. The abundances of Phytoplankton were also considered. The results of the water quality index (WQI) calculations during this study showed that the drop in Lake water levels led to a decline in the water quality of the Lake and Khors from the order of good to medium. Also, the trophic state index (TSI) values revealed that the productivity of the Lake changed from mesotrophic during high water level to eutrophic during low water level. These results are consistent with high phytoplankton counts recorded during low water level period. The values of N/P ratios indicated that phosphorus controls the phytoplankton growth during high water level, while during low water level either phosphorus (P) or nitrogen (N) could be limiting phytoplankton growth. Based on the obtained results of the present study, it could be concluded that the drop in water level upstream the dam may have negative impact on the water Quality of the Khors. This impact may in turn influence the whole Lake due to water rebounce from the Khors to the main channel. Therefore, it is further concluded that khors could be considered as potential pollution sources during low water levels of the lake.