Largest underwater effects tank

The largest underwater effects tank is based at Leavesden Studios near Watford in the UK. The tank, which was built to facilitate filming of the underwater scenes in Harry Potter and the Goblet of Fire (UK, 2005), is 6 m (19 ft 8 in) deep, 20 x 20 m (65 ft 7 in x 65 ft 7 in) wide and incorporates a viewing chamber and ‘dry area’ for actors and crew. It took 50 construction workers three months to build and holds 2,273,046 litres (500,000 gallons) of water which can be filtered in under three hours. The water is 50 per cent ultra-violet filtered and 50 per cent chlorinated, which means actors can remove their goggles during filming without irritating their eyes, allowing them to focus better and act to camera. Considering Harry Potter wears glasses above ground but can see perfectly well under water – now that’s magic!