This area was used as a source of sand and gravel for the three million tonnes of concrete in the Warragamba dam, 19 Kms upstream, built 1948 - 1960. There was an overhead conveyor running from here to the dam site, and there are a few relics of this era still visible. The lagoon to the northwest of the main channel is a result of all this. I discovered when I started to geotag my pictures that it is possible to walk right round this lagoon, although the track is not as obvious on the ground as on the aerial photographs and involves some careful trespassing. But all in the name of photography and healthy exercise. Look at the geotags.