Lake Tana water resource is of crucial importance serving multiple purposes and having largest surface area with fresh water body in Ethiopia. However, Lake Tana is facing water quality problem due to pollution caused by anthropogenic influences. This study was undertaken to assess water quality of the Southern gulf of Lake Tana using indicator microorganisms and some physicochemical parameters. A total of 48 water samples were collected from water of Southern gulf of Lake Tana. In this study, sites were selected purposely and sampling was taken seasonally dividing into wet and dry seasons. Indicator microorganisms (total and fecal coliforms) and some physicochemical parameters such as pH, Temperature, EC, TDS, Turbidity, NO 3 , DO and BOD5 were determined to estimate pollution status in different sites. In the present study, total coliforms and fecal coliforms were enumerated using a multiple tube fermentation technique with MacConkey broth as the presumptive medium, eosine methylene blue (EMB) agar as the confirmatory medium. In this study counts of fecal coliforms were 1 MPN/100ml to 1600 MPN/100ml with lowest and highest mean value of 1MPN/100 ml at S8 to 1076.5±3.1 MPN/100ml at S4 with significant p<0.05 and total coliforms counts were also ranges 1 MPN/100ml to 1600 MPN/100ml with mean value of 4.8±1.81 MPN/100ml at SR6 to 1600 MPN/100ml at S4 and SR8 with significant p<0.05. Most of high count of total and fecal coliforms in this study was recorded during wet season. Physicochemical parameters of this study showed that some of parameters were under the group that made the lake was not polluted, but some parameters where in the group that informs the lake was deteriorated. Although there was significant variation in most of the physicochemical parameters on season and sites, some of the physicochemical parameters were insignificant to sites and revealed some contamination both dry and wet seasons. Generally, southern gulf of Lake Tana water also showed that some of the parameters were within the limits of USEPA and EEPA some were exceeded the limits which depict occurrence of pollution. Therefore, undertaking constructive management action and giving attention is needed for this anthropogenic interference which causing Southern gulf of Lake Tana water was polluted. Key word: Bacteria, Lake Tana, pollution, physicochemical, , PO 4, NH 4