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.
Keywords: Bioindicator; Biological Monitoring Working Party (BMWP); Chemical properties; Macroinvertebrates; Nile Biotic Pollution Index (NBPI); Water quality index (WQI).