الفهرس 
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Abstract
The present study aimed to follow the seasonal dynamics of waterborne pathogens (Cryptosporidium oocysts, Giardia sp. and Entamoeba sp. cysts) throughout one year (from January to December 2014) and to demonstrate the correlation between the occurrence of these pathogens and the physicochemical parameters of the influent of four water treatment facilities in Dakahlia Governorate, namely Sherbin, Belqas, Meet-Khamis and Al-manzala. Materials and Methods: water samples were collected monthly from each station. Water samples were filtrated through a membrane filter and subjected to physical, chemical and biological assessment. SPSS was used to compare the intensity values of parasites (Cryptosporidium, Giardia and Entamoeba) among the localities. The same software was used to reveal the relationship between the intensity values of each protozoan species and each of the physicochemical environmental factors. Results: A total of 218 (oo)cysts were encountered in the studied water samples using the routine iodine staining and light microscopy. The most common protozoan parasite detected was Cryptosporidium sp., followed by Giardia sp. and Entamoeba sp. Total numbers of (oo)cysts in different studied sites reflected that the intake of Meet-Khamies station had the highest intensity of parasites followed by the intake of Al-Manzala station, the intake of Belqas station and finally, the intake of Sherbin station. Seasonal variations in the count of parasites during the study period were shown to be highest during summer followed by spring, autumn and finally the lowest numbers were recorded during the winter months. Except for temperature and turbidity, all the physicochemical environmental parameters were found to reach their peak during winter and reach the lowest values during summer. Positive relationships were found between Cryptosporidium and Giardia, Entamoeba sp. and total coliform. Negative relationships were found between Cryptosporidium and ammonia, nitrates and potassium. Giardia attained positive relationships with Entamoeba sp. and total coliform. Negative correlations were found between Giardia and potassium, ammonia and nitrites. Regarding Entamoeba sp., positive relationships were found between this pathogen and both total coliform and pH. In contrast, negative correlations were detected between Entamoeba sp. and TDS, calcium, sodium, ammonia and nitrates. Conclusion: The occurrence of cysts/oocysts in raw water samples represents a potential risk to the public health as a result to being resistant to disinfection. Close and controlled management of water supplies during summer months is recommended in order to reduce waterborne diseases. In addition, protection of water resources enforced by laws regulation should be activated to limit water pollution.