Ms Austin, who has been a wheelchair user since 1996, developed the chair with help from dive experts and academics.
The model is powered by two dive propulsion vehicles and steered with a bespoke fin and foot-operated acrylic strip.
She is staging a performance with it in a swimming pool in Weymouth this week.
Creating the Spectacle forms part of the Cultural Olympiad celebrations.
Ms Austin, from north Devon, says she first had the idea after learning to scuba dive in 2005.
"When we started talking to people about it, engineers were saying it wouldn't work, the wheelchair would go into a spin, it was not designed to go through water - but I was sure it would," she told the BBC
via bbc.co.uk