Old movie, made in Australia?

old movie about a little town near a lake or swamp, all i remember was the monster was a backhoe, and there were milk jugs fastened to the bottom of the lake to imitate heads of dead people, they found this after draining the lake. i would like to know what this movie is called, i have searched 'back hoe' 'swamp monster' and other things on imdb.com and other sites and cannot figure out what it is called.