The water-dweller of Aboriginal tradition, known under many names across many nations, and consistent in one thing: the warning. Waterholes where the bunyip lived were not approached at night, and the bellowing roar from the billabong — a sound settlers later attributed to bitterns, seals, or nothing they could name — meant the warning stood.
Colonial Australia took the bunyip seriously enough that in 1846 a strange skull from the Murrumbidgee was exhibited in Sydney as a possible specimen (later assessed as a deformed foal's), and newspaper accounts of the 1840s–50s treat sightings as provincial news. Descriptions vary wildly — dog-faced, seal-bodied, emu-necked, tusked — which folklorists read as many water-dangers sharing one name.
The archive holds the bunyip as the type case of folklore doing safety engineering: whatever exactly bellowed from the billabong, the people who had lived alongside it for tens of thousands of years said don't swim there, and were right.