Kirralea Birch has found a novel way to beat the heat while entertaining the crowds at Fringe World by performing as a mermaid in an aquarium outside the Old Treasury Building.

She is one of six mermaids and mermen who each spend 10-minute stints duck-diving and cavorting in the tank in the temporary Treasure Chest outdoor bar for the duration of Perth's Fringe Festival. "It is the coolest job in town," Ms Birch said. "If you love being underwater, then it is just great. Everyone has been angling for it."

Outside, it has been so hot that someone's shoe melted on stage yesterday." Fringe World runs until February 19.

Ms Birch, of East Perth, said her profession as a photographic artist who specialised in underwater imagery had come in handy for the role, which required holding her breath for long periods.

"You also need to let the air out before you go down or you will float to the top."

The Treasure Chest has been built into a vacant lot between Perth Town Hall and the Old Treasury Building, the site where Perth was officially founded in 1829 by the felling of a tree