River passing through a park

Maps

Geoscience Australia provide downloadable topographic maps
50k Map Index, most from northern coastlines, minimal others
100k Map Index, most coastal regions excluding Tasmania
250k Map Index, complete coverage
1 Million Map Index, complete coverage

The Federal Government's National Maps is a useful online topological map with lots of additional data providers like the SRTM 1 sec DEM data set.

Sentinel Hub is a great tool for viewing near real time satellite data including Sentinel, Landsat, and other Earth observation imagery.

New South Wales (NSW)
Free PDF downloads or browse online. Mostly 1:25K, some 1:50K maps.
GetLost Maps
Free topographical maps that you can download directly from their website as well as on Avenza Maps.

Distance markers

The online map has markers every kilometer that start at 0 where the Macquarie meets the Barwon River up to 882 just before the source of the river at the Fish and Campbells River confluence. When entering the Barwon River, you are about 1,798.1 km from the ocean if you keep paddling down the Darling and Murray rivers.

Zoom in to see all of these markers. These do not correlate with any existing numbering system on the river.

    Refer to the Barwon River Maps page for the Darling and Barwon river distance markers.