...He then made the 'Awesome' sign. Yeah, I thought. Awesome. About twenty feet away, the pale, terrifying, instantly-recognisable shape of a shark cut through the water in a slow curve, around us and away. It was a 6 foot long, whitetip reef shark.

We spent the day diving on the Opal Reef – a popular spot on the outer fringes of the Great Barrier Reef - having caught a high-speed catamaran out from Port Douglas with a company called HABA. Diving in Australia is big business. In Thailand on Koh Tao, our boat was twenty feet long, had 4 instructors and 8 divers. HABA's cat was about 60 feet long, had 25 divers, 75 snorkellers and 3 instructors. And a buffet lunch.

We were on a strict timetable, so after the hour and a half commute out to the first dive spot (during which we spotted another humpback whale) we were suited up, striding in, and descending to 18 metres before we really knew what was going on. This haste was probably a bit too much for Sarah and me. My oxygen consumption was awful, and Sarah had to abandon her dive after 15 minutes as her ears couldn't equalise quickly enough. HABA were kind enough to give her an extra dive for free later that day though. Sarah was (and still is) very pleased with this, as it means she now has one more dive in her log-book than me, so is technically a more experienced diver. Whatever. Has she seen a shark yet? No.

Once we got down there, the dive was great. The variety and number of fish around us was incredible. We swam around towers of coral and over giant clams, through shoals of chevron barracuda and (my favourite) yellow-tailed fusiliers, and even spotted a few clown-anenome fish (a Nemo for Alex & Rex). I was told by some of the more experienced divers that the reef wasn't in that great a condition compared to Thailand or the Red Sea, but it's hard to take these kinds of comments seriously when you've just swum with a shoal of barracuda or rapidly away from a shark!