Tourist Map of Australia

While there are marshlands and swamps its a fairly minuscule amount of the land. Most of the North East is rain forest or sugar cane farms. Most of the central north is desert. Most of the north west is also desert.

For example

The Arafura Swamp is a large inland freshwater wetland in Arnhem Land, in the Top End of the Northern Territory of Australia. It is a near pristine floodplain with an area of 700 square kilometres (270 sq mi) that may expand to 1,300 km2(500 sq mi) by the end of the wet season, making it the largest wooded swamp in the Northern Territory and, possibly, in Australia.

For context the Northern Territory encompasses about 1.35 Million square kilometres.

So there should be more marked in black but really it wouldn’t be very noticeable at this scale.

I was thinking the same thing, there's definitely some more inland water-based dangers.