Having lived in Sydney for my whole life, I’ve often thought about what is actually going on underneath the surface of the harbour. For a while, I assumed that the harbour looked exactly like the inside of the aquarium- very blue and with lots of colourful fish. And then I learnt that there are tunnels that actually go under the water, which blew my mind and made me rethink my whole understanding of the world. And now, coming into summer, seeing huge cruise ships docking in Circular Quay every other week, I am still just as confused about how the whole thing works. Surely those ships are too big to not hit the bottom, and yet they never do.

To get some answers to these questions, I called on Professor David Booth from the University of Technology Sydney and a marine biologist at the Sydney Insitute of Marine Science.