Subsidence from underground coal mining is a problematic issue for stream and river managers in the Sydney basin. Our study investigated a small waterway that had been degraded by a coal mine longwall that made multiple passes directly under it. The most obvious impact was loss of stream flow through sections of fractured bedrock channel. Water quality of the stream was monitored over a 5-year period, at sampling sites where the creek had flow. Discoloured water appeared in some sections of the creek and background (upstream) conductivity increased by four times from <250 µS/cm to 1195 µS/cm in subsidence affected zones. The concentration of metals such as zinc and nickel increased by many times to levels exceeding the ANZECC water quality guidelines for aquatic ecosystems. The macroinvertebrate composition of sections of the creek was strongly impaired and mosquito larvae become highly abundant. Sampling was conducted at a site where upwelling groundwater entered the creek through recent subsidence fractures. Below this point the creek flowed continuously during the most recent six months of the study. Mean electrical conductivity increased due to that upwelling, rising 6.8 times from (230 µS/cm) at upstream/reference sites to 1806 µS/cm below the upwelling. Dissolved oxygen of the upwelling groundwater was extremely low (2.7 %) and was also acidic (5.8 pH).