In stage magic, the Aquarian Illusion is a variation of the Metamorphosis or Substitution Trunk magic illusion. It was created in the 1970s by Alan Wakeling for Mark Wilson, who performed it in The Magic Circus series and a HBO special Mumbo Jumbo! It's Magic, and in closing his Las Vegas shows.
The illusion begins with a large, lidded tank made of acrylic glass. The tank is filled with water and a swimsuit-clad female assistant climbs inside, takes a deep breath, and submerges herself. The tank's lid is closed and secured with padlocks and chains wrapped around the tank. The assistant is now trapped underwater, with no apparent source of air. This adds an element of peril; if something were to go wrong, the assistant (or magician) could possibly drown.
A curtain is lowered over the tank, concealing it from the audience. The magician ducks inside the curtain, then begins to count to three, showing his head from behind the curtain on "one" and "two". On "three", the assistant, not the magician, emerges from the curtain to call out the number. The curtain is then parted, revealing the magician now locked inside the tank.