The dingo (Canis lupus dingo) is a keystone species in Australian ecosystems. The current study reports four dingoes observed attacking a swimming eastern grey kangaroo (Macropus giganteus) in the Wollondilly River, New South Wales. It is proposed that kangaroos need to stand at a certain depth of water to escape an attack by dingoes. If dingoes can continue attacking from opposing directions without threat of injury from the kangaroo, such as in shallow water where dingoes can stand or deep water where kangaroos cannot stand, then the attack may continue until the predator(s) kill the prey or the prey escapes. Further research on such behaviours is needed to understand the functional role of dingoes and the importance of pack structure in development of hunting strategies.