In 1980 the sewerage system of the Blue Mountains (NSW) regional townships was inadequate. It included unsewered areas and the dozen overloaded treatment plants provided incomplete treatment that caused widespread pollution of streams throughout the region. Following a thirty year program to upgrade the entire sewerage system, one of the last major pollution discharges to be addressed was Blackheath STP, which was permanently closed in 2009. Freshwater macroinvertebrates were used to measure the ecological changes that resulted following its closure over a 15-year period. This began when it was still operating in 2003 to nine years after its closure in 2018. There have been few opportunities to study the recovery of an otherwise natural mountain stream ecosystem that had been chronically impaired by decades of being used for disposal wastes. We used a replicated quantitative ‘kick sampling’ technique and identified invertebrates to the family level to measure ecological health recovery of the small headwater stream. In addition to using an upstream versus downstream comparison, we also used an additional two nearby reference streams in naturally vegetated and undisturbed catchments. We calculated several biotic indices to assess ecological recovery over time. We found that the degree of ecological recovery was large but not complete, indicating a possible residual disturbance remaining. We suggest that one of the most important factors that has enabled the recovery to date was the very good water quality and environmental condition of Hat Hill Creek upstream of the pollution.