The reservoirs supports a number of mammal species including otters and badgers.  Although these are rarely seen, otter spraints have been regularly found on the Nant Fawr stream which runs through the site, and there is evidence of badgers foraging on the grasslands of the reservoir embankments.  The site is also extremely good for bats, and all three species of pipistrelle (common, soprano & Nathusius) have been recorded, as well as noctules, Daubenton’s bat and long-eared bats.  Although there have been no surveys of small mammals on the site, harvest mice have been recorded from the adjacent meadows and dormice are possibly also present.