Nine Bay of Plenty players have been selected for the squads, including six from Tauranga Underwater Hockey Club.
East Bay Club captain Mandy Shields, who is Simon's mother, said it was the greatest number selected from the region in years, and made a welcome change from the usual Auckland/Wellington dominance.
"Mostly we have had two or three in the last couple of years," she said. "In our region, it [underwater hockey] is getting more known, and we're building numbers which is fantastic."
All selected players will be pay their own way to Spain.
Underwater hockey was developed in Britain in 1954 by Alan Blake as a winter activity for scuba divers to keep fit.
A challenge for even the most experienced swimmer, it has since become a global sport.
Similar to other forms of hockey, players use a stick to play a puck around the field - but in this case, the field is the bottom of the pool, and teams are kitted out in diving masks, snorkels, and fins.
Mrs Shields said it was a highly competitive game that required a large lung capacity.
Simon Shields said he had taken up the sport in Year 10 after being introduced to it by a friend.
"It's a different sport all together," he told the Rotorua Daily Post yesterday. "I've always enjoyed swimming and watersports, and I just took to it."
These days, Shields trains in the pool several times a week, and plays underwater hockey matches in Rotorua and Tauranga for Eastern Bay Underwater club. He thought he could swim up to 75m before coming up for air.
The trip to Spain will be the furthest Shields has ever travelled away from New Zealand. He is excited about the tournament, but didn't want to make too many predictions about the final outcome.
"I wouldn't know until I play really. I hope so, but I don't want to make any promises."
-East Bay Underwater club will be hosting the North Island Underwater Hockey Club Championships at the Rotorua Aquatic Centre over the Queen's Birthday weekend ( May 30-June 1).