The 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.