Duhok dam reservoir is situated in Duhok city, Iraq. It is an artificial reservoir which supplies water for crops land and orchard around the canal throughout its path. The objective of this investigation is to assess physical, chemical and microbiological aspects of aquatic ecosystem in the lake. The water quality variables (water temperature, pH, EC, total dissolved nitrogen and phosphate, SO 2 , BOD 5 and microoganisms) were being measured seasonally during 2011. The results reported that high conductivity and sulphate concentrations were recorded during different seasons. Heterotrophic plate count and faecal colifom exceed Iraqi and WHO standards for drinking purposes. Statistically, no differences were found between studied sites for all variables. Microbiological isolates, counts, total occurrence and diversity index were more in sediment than in water samples. The occurrence of mycobiota was surveyed by three isolation methods 19 fungal species assigned to 14 genera were isolated. The most frequent species in order were: Aspergillus spp., Penicillium spp. and Eurotium spp. The occurrence of keratinophilic fungi was detected in the sediment by hair baiting method The most frequent genera isolated in this study were Chrysosporium spp. , Trichophyton spp. and Microsporum spp.