Water is one of the natural resource that used for irrigation, industrial, sanitation and other purposernthat facilitate human activity. Lake Beseka is volcanically dammed, endorheic lake, which isrnlocated to the East direction, situated around 200 km from Addis Ababa, the capital city ofrnEthiopia. The Lake water is saline and alkaline with high concentration of fluoride so that the waterrncould not be used for drinking and irrigation purpose. Different infrastructures such as a healthrncenter, high school, youth center, offices and others were affected by the lake flooding. So, thisrnlake needs to be treatment. rnIn present study, biological neutralization of saline- alkaline beseka lake water in the presence ofrnglucose (carbohydrate) as carbon source was studied. To do so, determination of physiochemicalrncharacteristics of the lake water, which was pH, EC, TDS, HCO3rn-rn, total alkalinity, chloridernand fluoride were measured and also isolation of bacteria were carried out. In this study Bacillusrnalkalophilus bacteria was also used to compare its treatment performance with isolate (T1).rnTreatments of lake water sample at different pH, incubation time and inoculum size werernmonitored. Maximum removal of total alkalinity and TDS (Total Dissolved Solid) were observedrnat pH, incubation time and inoculum size of 9,72hr and 32ml respectively. Which is resulted inrnremoval of total alkalinity; 774.669mg/l and TDS;1939.92mg/l for isolated (T1) and totalrnalkalinity;779.631mg/l and TDS;1944.97mg/l for Bacillus alkalophilus from original value. Basedrnon these findings, isolated (T1) bacteria were shown to be have good performance for biologicalrntreatment of beseka lake.