There has been at least one fatal shark attack in the Swan River over the years, and a few non fatal.
They are from bull sharks which take a liking to swimming up the river and have been responsible for attacks as far up as the Garret Road bridge near Guilford.
For some reason they call them Swan River Whalers but they are a type of bull shark.
They don't rip you to bits like a great white because they are not big enough for that, but they can chew a sizable hole in your arm or leg so that you die from rapid blood loss.