Large amounts of sewage and industrial effluent are released into water bodies on a regular basis. This has greatly contributed to the contamination of surface and ground water. The current study's goal was to evaluate the Ribb River's water quality. The Ribb river is one of the biggest river in Ethiopia. This river plays a vital role for socio-economic structure of the country development. Therefore, this study focusses on the assessment of physico-chemical water quality parameters of Rib River water from the source to the receiving Lake Tana. Samples were collected 3 times at each 10 different places in two seasons (dry and rainy) and analyzed using physicochemical water quality parameters including Temperature, pH, EC, TDS, TSS, DO, salinity, turbidity, BOD, TS, Nitrate (NO3 - ), and phosphates (Po4 3- ) and compared with surface water quality standards using standard procedures. Temperature and pH were measured on site with a mercury thermometer (range 0˚ to 100˚C) and a digital portable pH meter, respectively. The mean value of such respective parameters in both seasons were compared with the water quality standards. Analysis of variance (ANOVA) using SPSS was carried out to determine the significant differences. Estimation of quality status of water were done by using WAWQI. Among the all tested physical parameters; Temperature, EC and TDS, were with in the standard level. On the other hand, in chemical analysis it is found that, DO, salinity, BOD, and phosphates (Po4 3- ) were under the permissible amount. Turbidity, TSS and Nitrate (NO3 - ), exceeds the permissible amount. The overall test results reveal that the quality of Ribb River water is under poor quality status. This leads to pollution of lake tana. Thus, the government need to take proper steps to control the effluent discharge to the river.