In regulated rivers environmental flows (the provision of water to maintain ecosystems) are the main management technique used to ameliorate the ecological effects of flow alteration. In 2010 a new environmental flow regime based upon translucency and transparency rules was put in place in the Hawkesbury-Nepean River system by Sydney Water Corporation. For the transparency component all inflows to the dams are released up to the 80th flow percentile. For the translucency component 20% of the flows above the transparency threshold are also released. In autumn 2013 I sampled macroinvertebrates from edge, pool-rock and “riffle” habitats in 21 regulated and unregulated sites that had been previously sampled between 1995 and 1997. In the 1990’s there was a clear impact of river regulation on the macroinvertebrates in those habitats. Most analyses of the new data indicated that there were no significant differences in either the pool-rock or “riffle” macroinvertebrates between the unregulated and regulated sites in the 2013 samples. These results indicate that the environmental flows have resulted in ecological improvement. However, more sampling occasions and results from the edge samples are required to confirm.