Physical, chemical and biological qualities of 28 man-made mountain reservoirs in the Jabal Akhdar area were studied. Of these, 10 are old traditional reservoirs, while 18 are newly built modern reservoirs. The physical and chemical quality of the water as determined by 19 parameters were compared against the Oman, WHO, EPA and EC standards recommended for drinking water. All important parameters with the exception of pH and conductivity were well within the safe limits. Even the pH was unacceptable in eight reservoirs and the conductivity in two reservoirs only. However, eutrophication appeared to be a serious problem in all reservoirs and using an eutrophication index, all the reservoirs were eutrophic. In the absence of natural flushing by floods, these reservoirs are bound to suffer from eutrophication associated impacts. Fecal contamination of these reservoirs from both animal and human sources is significant. The prevalence of fecal coliforms and Escherichia coli showed that the water from these reservoirs is of unacceptable quality. This study also attempted to relate biological diversity to water quality. The rough guideline suggests that all reservoirs are moderately or heavily polluted. The socio-economic implications of the newly built reservoirs include several benefits and some drawbacks. These reservoirs are not primarily used for drinking and management strategies need to be developed to combat eutrophication and to improve the microbiological quality of water.