He won a silver medal in the 10 km race at the European Open Water Swimming Championships in 2016 but was disqualified during the same event at the 2016 Olympic Games.

[3] In the men's 10 kilometre open water event, he was disqualified after receiving two yellow cards for unnecessary contact with other swimmers, though he initially appeared to have finished fifth alongside Marc-Antoine Olivier and Zu Lijun.

[6][7] In an angry interview following the race, Burnell claimed that Mellouli had grabbed his leg and that it may have stopped him from winning, and said the first card for unnecessary contact had been awarded when there were no other swimmers around.

Ahead of the World Championships in Budapest that year, he revealed that he had been struggling with "nightmares and depression" since the 2016 Olympics: "Sometimes I forget and I don't think about it for a few days, but then there'll just be something that triggers the memory.

[3][10] Burnell finished 24th at the Doha World Cup in March and then announced his retirement from the sport the following month, ending his bid to reach the postponed Tokyo Olympic Games.