Stinger season is between November - June each year. There are 2 crocodiles living at the mouth of Myall Creek and crossing the mouth is neck deep so I dont recommend trying that. The crocs wont chase you along the beach, if in doubt ask a local.
I'm sure you've heard about the deadly Box Jellyfish. The water may look welcoming, but you really don't want to go swimming between October and April when the jellyfish are most prevalent.
There are signs like this one warning you about the dangers and there should be some vingear as well just in case someone's unfortunate enough to get stung.
During the wet season marine stingers are very common in the beach, so swiming is not a good option.