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.

Have you tried Insight Genesis. they have maps for lakes all over the world. I fish St Georges Basin NSW and have downloaded a map that shows the water depth in 1ft. increments. Shows up all the gutters, channels etc. I can use it in my Lowrance sounder. Makes finding the Flathead on the dropoffs so easy.
Check this link.   https://www.genesismaps.com/SocialMap