A family fishing trip on the popular Bohle River, Townsville, recently resulted in an unusual experience. A large popper bottle , with cord attached , was noticed floating along with the incoming tide . For some strange reason , fish frequently erupted near the bottle . Then , oddly , the bottle began to travel against the tide and move towards the bank , again causing fish to leap , as if being chased, frightened . The mystery was solved when the head of a large crocodile broke the surface near the float . The theory is that the crocodile had grabbed a mud crab pot and had been trying to get at the meat bait inside the trap to which was attached the cord and bottle .