Each year thousands of British holidaymakers trek across the world to scuba dive on pristine coral reefs anywhere from Australia to the Maldives. But coral reefs are under serious threat globally. Destructive fishing practices, ocean acidification and sedimentation are taking their toll. Scientists estimate that almost a quarter of the world's coral reefs are already damaged beyond repair. If trends continue 70% of coral reefs could be destroyed in as little as 50 years, according to the US-based Nature Conservancy.
The biggest threat to coral reefs remains rising sea temperatures from global warming, and unfortunately the long-haul flight to the Barrier Reef or the Bahamas is probably the most damaging thing a tourist can do to the reef.
Padi, the world's largest diver training organisation, provides guidelines for eco-tourists and courses in sustainable dive practice through its Project Aware. There are a few simple steps tourists can take - practising buoyancy control skills before diving to avoid accidentally kicking the reef, never standing on or collecting coral - to avoid causing damage.
But not all diving has to be in crystal-clear tropical waters. Britain has some fantastic diving along its coastline, with thousands of wrecks to explore and a huge diversity of sea life. Brighton and Weymouth are busy harbours for Channel diving and the Farne Isles - 28 rocky outcrops in the North Sea off the Northumberland coast - are popular for their seal colony, sheltered coves and shipwrecks.
Some of the most popular dive sites are listed at ukdiving.co.uk along with scuba clubs and commercial operators.
If warm waters beckon there are plenty of places to dive in the Mediterranean, which can be travelled to without flying. Or you can put your diving holiday to good use on one of the hundreds of marine conservation projects that need volunteers. Responsibletravel.org have a coral reef conservation holiday in Honduras in March and April 2007. Marine conservation projects in Scotland, Fiji, Thailand and the Seychelles are also on offer.