Hypolimnial releases from dams during periods of thermal stratification modify the downstream riverine thermal regime by decreasing water temperature and reducing natural diel thermal variability. This cold-water thermal pollution in rivers can persist for hundreds of kilometres downstream of dams and impact important ecological processes such as fish spawning. To mitigate this problem, a first-of-its-kind thermal curtain was fitted to the large bottom release Burrendong Dam on the Macquarie River, Australia. The thermal curtain acts by directing warmer, near-surface epilimnial water to the low-level hypolimnial offtake. This study aimed to test the efficacy of the thermal curtain by measuring temperatures before and after the curtains installation, quantifying the magnitude and extent of cold-water thermal pollution along the Macquarie River downstream of Burrendong Dam. Epilimnial releases with use of the curtain increased diel temperature ranges and the mean monthly water temperature below the dam. Epilimnial releases with use of the curtain increased diel temperature ranges from 0.9°C to 2.5°C and reduced the difference between the mean monthly water temperature of an upstream control and a downstream site by up to 3.5°C. A comparison of the monthly temperature means along the river, indicated that thermal recovery, whereby temperatures returned to within the natural range of upstream temperatures occurred 45 km downstream of the dam during summer when the thermal curtain was deployed, compared with approximately 200 km prior to deployment of the curtain. Our study suggests that the use of thermal curtains can reduce cold-water thermal pollution and improve ecological outcomes for river ecosystems downstream of dams.