Coal mine operations often generate large volumes of waste water which are commonly disposed of to local waterways. Environmental regulations govern the discharge of waste water and may fail include a range of potentially harmful toxicants. Mine waste water discharges are commonly contaminated and, when released to receiving waterways, can be ecologically damaging to downstream aquatic ecosystems. This study investigated the effect of mine waste water discharges originating from a colliery in the south west of Sydney. The study investigated water quality and invertebrate populations in both the receiving waters of the discharge stream and upstream and downstream of the confluence with the Georges River. The mine waste water discharge is highly saline, alkaline and enriched with heavy metals, and as a result significantly changes the water chemistry of receiving waters. Water quality data was collected over an intensive one-month sampling period and incorporated with additional monitoring data published by the mine operator as required by the mine’s environmental protection licence. Results show mine discharge increased salinity in the Georges River from 160 µS/cm above the confluence with the discharge to 1108 µS/cm downstream of the confluence. Additionally, alkalinity and pH of receiving waters increased. The concentration of copper, aluminium, zinc and nickel in the Georges River was increased by the mine discharge to levels well above ANZECC ecosystem protection trigger values. This study also investigated the impact of the mine discharge on stream ecosystems using freshwater macroinvertebrates as indicators of ecological integrity. Quantitative collection of multiple macroinvertebrate replicate surveys were conducted using a rapid field based technique within the receiving stream, and in the Georges River upstream and downstream of the mine discharge. The invertebrate community recorded in this study show the mine waste water discharge had a major adverse impact on macroinvertebrate community structure with many sensitive groups that were present above the mine missing in the receiving stream and below the confluence. We make suggestions about how this case study can be used to generate quick, economical and robust chemical and ecological data to measure point source impacts from mines and other waste discharges.