Adelaide Icons and Cusps

Mike Rann says the Torrens Lake is an "Adelaide Icon".
What about the Lower Lakes? ......... World Heritage??

And whilst I'm at it, just how long is a cusp and when does it begin?
"South Australia is on the cusp of a mining boom" - source Mike Rann.
Perhaps it's like a length of string, hard to distinguish the beginning from the end.
Spin Spin Spin!