الفهرس 
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Abstract
Seasonal variation of air temperature has a great impact on Lake Nasser water. Water temperature in the lake; regulates the seasonal stratification and turnovers of the lake and consequently affects the physical and chemical properties of the lake water. Temperature cycle in Lake Nasser revealed that it is a warm monomictic lake where turnover occurs one time annually. The stratification period of the lake extends from spring (May) to summer (July). During this period, water temperature, dissolved oxygen, pH and sulfate values were decreased in the hypolirnnon while chemical parameters such as nutrients, BOD, COD, calcium and magnesium hardness, chloride, iron, manganese and total dissolved solids were detected with high values. However, in the epilirnnion layer, micro and macro-nutrients were greatly depleted. In turnover period which, extends from autumn (September) to winter (December), mixing occurs and water column is found to be isothermal at the end of this period. This process re-oxygenates the water layers of the lake and moves nutrient-rich water from lower layers to the upper layers. Moreover, calculations of average water quality index (AWQI,) during stratification and turnover periods revealed that the quality of water in Lake Nasser is improved during turnover and mixing periods.