Having lived in Sydney for my whole life, I’ve often thought about what is actually going on underneath the surface of the harbour. Going over the bridge and looking down below, or seeing the waves hitting the walls near Circular Quay, I’ve been very interested about what is actually going on below the shoreline. After visiting for my seventh birthday, 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. How did they build tunnels underwater without the whole thing flooding? To a twelve year old Lachlan driving through them every other week, this was a real concern! And now, coming into summer, seeing huge cruise ships docking in Circular Quay, I am still curious about the harbour. Surely the water can’t be so deep that these ships aren’t hitting the bottom! What is actually going on down there?

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. He explained how deep the harbour actually is, what kinds of animals are living there, and how it has changed as the city around it has evolved.