Hey mate,
I've been using an app on my Android phone/tablet for many years.
It's called Navionics Australia & New Zealand.
I quite like it and it shows all the water depths and structures and you can also use it to navigate your boat or kayak to likely fishing holes.
It's not free - I think I paid about $20 for it. But I think it's worth it, I use it a lot if I look for potential fishing spots in new areas.
In New Zealand there are also free marine charts available online. Not sure about Australia.
But the app is pretty good I reckon.
a snapper a day keeps the doctor away