Yondock is the great ancestral crocodile of Whadjuk Noongar tradition. In the Nyitting, the cold-time Dreaming, Yondock travelled down from the north country, disturbing and flooding the land: its passage let salt water into the Derbal Yerrigan (Swan River) and shaped Derbal Nara (Cockburn Sound), Wadjemup (Rottnest Island) and Ngooloormayup (Carnac Island). The Waugal, guardian of the fresh waters, smelled the salt, came down the river, fought and killed Yondock, cutting off its tail and setting it as the limestone bar at the river mouth at Walyalup (Fremantle) to divide salt water from fresh. The story, recorded from Whadjuk custodians including Trevor Walley and Teresa Walley, remains central to the cultural significance of the Fremantle area.