"This is a fierce creature from Australia. Amphibious by nature, it has the appearance of a giant seal or even a hippopotamus, It is greatly feared, for it enjoys the taste of human flesh, particularly the more tender flesh of women and children." quote from here.
The above black and white watercolor painting of one of these beasts is from 1935, artist unknown.
Additional links concerning the creature can be found here here and here.
And an illustration of a Bunyip or an oversized dog ruining the chest cavity of a swimmer.