Surface water has been under increasing threat of pollution in recent years due to improper management of vast amounts of waste generated by various human activities. Improper dump sites have served for many years as the ultimate disposal site for all types of waste: municipal solid waste, industrial sewage, and hazardous waste in developing countries such as Ethiopia. Physical, chemical, and biological processes interact simultaneously to bring about the overall decomposition of the wastes. One of the by-products of this mechanism is chemically laden leachate, it is a potentially hazardous waste from waste disposal sites. If not dealt with properly, such kind of dumping sites can cause pollution to surface water (through contaminant transport by flooding and groundwater movements). Therefore, this study investigates the spatial and temporal variation of ground and surface water quality within the Chilanchil Abay watershed during dry and wet seasons due to the waste disposal site of the Bahir Dar city. Water samples were collected from five sampling points of surface water from 30th March to 20th August by a monthly period. Over 15 water quality parameters such as pH, TDS, electrical conductivity, turbidity, temperature, DO, TH, BOD, COD, TC, NO3-, PO43−, Cr, Mn, and Pb were analyzed for surface water. It was found that water quality parameters such as TH, BOD, COD, NO3−, Mn, and Pb were within the acceptable limit, while the remains fluctuated depending on the sample period. The water quality analysis results show that spatial and temporal variation has a significant effect on the distribution of physical-chemical, microbial, heavy metal, and nutrient parameters along the watershed.