Nicholas, who has trained in swimming pools since he was nine, took part in his first open-water race - by chance - only two years ago.

'My club, Dik Wing Association, needed someone to swim in a race, organised by the Hong Kong Amateur Swimming Association, to gain some ranking points, so they sent me,' he says. 'I didn't train for it, but, surprisingly, won my age-group race. I started competing after that.'

Racing in the sea poses different challenges, he says. 'In a pool, swimmers race in their assigned lanes, but it's totally different in the sea. People can crash into you as the currents and winds are changing, so in the sea you need to constantly change your strategy.'

Besides regular training, good pre-race preparation is also a key part of success, he says. 'Before the New World Harbour Race, I took a ferry from Lei Yue Mun Sam Ka Tsuen public pier to Sai Wan Ho, which follows a similar route to the 1,800m competition. It's impossible to jump into Victoria Harbour to try the route before the race, but on the ferry, I could see the direction of the sea currents and feel the wind's direction, which was useful.'

Such careful preparation helped him to win the boys' (12 to 16) youth event in last October's race.

Nicholas is trained by his school's head coach Zhang Diyong, the former mainland swimming champion, who also coaches Hong Kong's freestyle record-holder Stephanie Au Hoi-shun, 20. Stephanie - a former student at Sacred Heart Canossian College who is now studying at the University of California, Berkeley, in the US - will be competing in her second Olympics this summer.

Nicholas trains only two hours a day - much less than other top swimmers - at Hin Tin Swimming Pool in Sha Tin. 'As a DSE [Diploma of Secondary Education] examination candidate next year, I don't have the time to do more training,' he says. 'So instead I'm boosting the intensity of my training and it's working quite well.'

Even though the 2013 East Asian Games and 2014Asian Games have no open-water events, Nicholas has a good chance of competing at both events; he is Hong Kong's second-fastest 400m freestyle swimmer - a feat he achieved at April's Festival of Sport - Olympic Time Trial II.

'Open-water swimming has helped me to swim faster in the pool,' he says. 'I've now got better endurance and consistency - and greater determination.'

Nicholas will take part in the fourth Xiamen-Kinmen Crossing competition on July 15 - a sea race from Kinmen Island to Xiamen , known for its big waves and rough seas. It will provide a good test before the World Championships.

'It's my first cross-strait race,' he says. 'It's the ideal warm-up for Canada, where I'm hoping to win a medal.'