There are always black snakes and tigers around the water here, I'm happy enough to keep my distance, though the blacks sure love a dip and I have been surprised a few times by a few passing by. I see heaps of platypus around too as some of these gold streams/creeks happen to be good trout streams/creeks as well, they are so bad sometimes I just skip the pools they are in knowing I have zero chance of taking a fish from them.
Last time I was out Sunny Corner I jumped 2 feet seeing one of those "toe pincher" water scorpion critters near my feet, I know they are harmless but it was the biggest I have seen, round here though its the tiger leeches that will carry you away if given a chance, especially out Oberon way.
We all know about snakes, but you need to be just as wary of dehydration and heat while out prospecting, also don't forget the bastard mosquito, Ross River, Barmah Forest and Kunjin Virus are not to be taken for granted, my cousin had Barmah Forest and was never quite right from it.
On a side note I brought Malaria back with me from a trip to Papua New Guinea, holy crap that floored me, I pretty much blacked out 2-3 months of my life going through that.
I remember going to the cinema the day after coming home and passing out from the fever, woke up in hospital, my mates thought I was just quiet watching the movie until the credits rolled and the lights came on! I was fine going through customs and immigration etc, had no idea at the time.