Mike, rather than fungus/moss/etc I suspect this is one of the tiny, vascular aquatic plants - in the duckweed line or similar. Have a look through the aquatic plants on CNM to see if you can find a possible match. The only moss/liverwort' candidate in such a habitat is Ricciocarpos (https://canberra.naturemapr.org/Community/Species/Sightings/15582) and I don't see that lobed structure in your photos.