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Rosetta and Damietta are the main branches of the Nile River in Egypt. They provide the required freshwater for different usage for about 20 million people. In the present study, chemical and biological indices were used to assess the water quality and provide a full image of the environmental status in the investigated area. Generally, the chemical parameters, except the dissolved oxygen, were at higher levels in Rosetta Branch when compared to Damietta Branch. Also, Damietta Branch frequently showed the presence of the macroinvertebrate families that are bioindicators of moderate and good water quality. Contrarily, the most resistant species to pollution were frequently recorded in the Rosetta Branch. According to Canadian WQI, the water of Rosetta Branch is classified from "marginal" to "poor" for the drinking and aquatic life uses and "fair" to "good" for irrigation usage. On the other side, the water quality of Damietta Branch is classified as "fair" with respect to drinking water and "good" to aquatic life and irrigation. Based on using macroinvertebrate families as bioindicators, the Biological Monitoring Working Party (BMWP) index and the Nile Biotic Pollution Index (NBPI) indicated that the water quality of the Damietta Branch was within "moderate" class, while Rosetta Branch is categorized from "very polluted" to "extremely polluted" classes. The results proved that both BMWP and NBPI have coincided with the CWQI for the drinking and aquatic life indices (p < 0.0001) indicating the validity of BMWP and NBPI to assess the water quality of the investigated area.

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This study focused on the monitoring and assessment of aquatic ecosystem functioning based on the abiotic and biotic features of Lake Nasser in the post-flood and pre-flood periods as the last ones before water storing behind the Grand Ethiopian Renaissance Dam. The physicochemical parameters, distribution and structure of biotic communities, including bacteria, phytoplankton, zooplankton, macrophytes, epiphytes and fish were analyzed at 15 sites. The values of most parameters (primarily temperature, total suspended solids, pH, orthophosphates, carbonates, sulphates and some cations) were higher in the pre-flood period, whereas higher values of conductivity, total dissolved solids, total solids, nitrites, nitrates, chemical oxygen demand, bicarbonates and chlorophyll a were recorded in the post-flood period. Cyanobacteria-dominated phytoplankton and total coliform bacteria were more abundant in the pre-flood period, and especially at sites 10–15, whereas higher abundances of zooplankton were recorded in the post-flood period. All these changes in parameters were significantly differentiated, and only the concentrations of dissolved oxygen, biochemical oxygen demand, ammonium and silicates were at similar level in both periods. The study also indicated that environmental factors had affected the macrophyte distribution and the adaptation of the invasive species Myriophyllum spicatum to thrive under different environmental factors in the lake. Besides, macrophytes provided the habitat to other aquatic organisms, especially epiphytes, and also helped maintaining the good water quality, nutrient cycling and stabilizing rivers' and lakes' banks. Generally, these conditions were rather favorable for biological processes and fish production. [ABSTRACT FROM AUTHOR]