Elias Akseli was riding a jet-ski when he collided with a jet-ski operated by a family member at about 4pm, The Phuket News was told.
Mr Akseli suffered an injury to his lower left leg and was quickly brought to shore by lifeguards and Royal Thai Navy water safety officers stationed at the Tourist Rescue Centre at Kata.
After a emergency rescue team applied a splint to his leg, Mr Akseli was taken to Phuket International Hospital for further treatment.
The Phuket News has yet to learn what damages Mr Akseli and his family will be asked to pay as compensation to the jet-ski operator.