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The Otago Boys' High School pupil claimed a treble of gold medals in the under-18 grade at the South Island secondary school rowing championships at Lake Ruataniwha.
Mason finished in 7min 30.02sec to edge schoolmate Thomas Ryan in the single sculls by a second.
John McGlashan College's Nic Chamberlain followed in third.
Mason then teamed with Ryan to sneak past Chamberlain and Will Turner in the double sculls.
Only 0.06sec separated the crews, but Mason and Ryan crossed first in 6min 56.58sec.
In the coxed quad, Edward George, Jack Webber and cox Jake Burgess joined the duo to complete the treble of golds for Otago Boys'.
Dunstan High School's girls teams also continued their success by grabbing five golds.
Sophie Smith and Malia Banks won the under-15 double sculls, before Phoebe Wellstead, Brooke Williams and cox Chloe Robertson joined them to win the quad.
That quartet also made up half the octuple sculls crew which blitzed the field to claim a third gold in the grade.
It had similar success in the under-16 grade.
Mackenzie Ealson and Paige Furrie claimed the double sculls, while Hanna Scarlett, Erica Morris and Lauren Grey joined them to win the quad.
Dunstan added a silver and two bronzes to finish fifth on the overall points table.
Columba College and St Kevin's College won the other two golds by Otago schools.
Columba's Antonia Bachop, Niamh Paterson, Sienna Snow, Amelia Findlater and cox Ella Herbert combined to win gold in the under-16 girls coxed four.
For St Kevin's, Annie Metcalfe, Jaimee Trainor, Ruby Bradley, April Linares-Fontona and cox Ruby Macauley claimed gold in the under-18 novice coxed four.
John McGlashan's Angus Kenny won two silvers - in the under-17 single sculls and under-18 double sculls.
He was also part of the crew which won bronze in the under-18 coxed four.
The other three to win single sculls bronze medals were Hannah Cunningham (St Kevin's, under-17), Eva Hofmans (Bayfield High School, under-18) and Sophie Smith (St Hilda's, under-16).
Smith also won double sculls silver with Millie Davenport.
Sophie Sinclair and Ella Fry made it three for St Hilda's with a silver in the under-18 double sculls.
Mount Aspiring's novice duo of Pipi Horan and Ruby Boyd won silver and were joined by Hayley Ambrose, Emily Findlay and Patrick Hartley to repeat that placing in the quad.
The same four also combined to win silver in the under-15 quad.
Holly Dalzell and Jordin Robinson got Cromwell College on the board with silver in the under-17 double sculls.