If you lived in the northern hemisphere of Australia I think you would be risking it in a float tube and end up entree for some croc, as most rivers have a resident bitey living in them. Great Whites are a problem in the south in some areas, more so in South Australia and Western Australia. I live metro Adelaide and we get the occassional shark in close to shore during the summer months especially around the in shore reefs along the coast line, one just has to use a bit of sense. Most common sharks are the occasional thresher, a few school shark and mostly bronze whalers
I wouldn't drag a bag of fish behind me if I could help it.
I usually fish off man made structure in the open water but we have a few local rivers that produce good bream and mulloway and smaller species such as mullet and Australian salmon.
Must admit though that most places you go around here has got some sort of bitey looking to get you if you are not careful, like snakes or centipedes/spiders.
I think most aussies as kids get it drummed into them by mum and dad to watch where they walk if out in the bush, but even then we get the odd snake in the back yard sometimes,not to mention redback spiders in the south of Australia or funnel web spiders around sydney. Apart from the red back everything else automatically wants a piece of you.LOL.
It's not as bad as I make out, you just have to be careful.
I suppose it's relative to where you live, I see the States as somewhere where if you go river fishing a bear will get you, or a rabies infested raccoon will hunt you down.LOL