Unless tour operators specifically start taking sustainability seriously, then they are really beginning to kill the goose that lays the golden egg

WWF spokesman

Mr Woolford said the scarce water and energy resources of the region were also being severely overstretched.

The WWF is urging tour operators to take a more responsible approach and give their customers more information about the steps they can take to protect the Mediterranean environment.

New analysis from the fund shows that countries like Morocco, Tunisia, Greece, Turkey and Croatia will undergo rapid development.

Serious message

Mr Woolford said that the Germans visited Mediterranean resorts in the greatest numbers, followed by the British.

Monk seals are threatened by pollution and sewage

He said that tour operators were in danger of losing the very source of their wealth if they continued to ignore environmental issues.

"Responsible tourism is a very easy message for holiday-makers," he said. "But for the industry, it's a much more serious message - it's about looking after the sort of natural base on which the whole business depends.

"And unless tour operators specifically start taking sustainability seriously then they are really beginning to kill the goose that lays the golden egg."

Mr Woolford suggested providing customers with more information about environmental issues and cultural sensitivities at their destinations. And he said tour companies, particularly the larger ones that owned hotels, should take eco-efficiency measures such as saving energy and water.

Confused turtles

The WWF said that many areas in the region important for nature were also among those threatened by tourism growth.

WWF wants tourists to be aware of environmental issues

Spain's Balearic Islands, popular with Britons, are also habitats for sperm whales and sea turtles.

Newly hatched turtles are particularly in danger, being attracted by the bright lights of hotels rather than swimming out to sea.

Turkey's Anatolia coast is the home of Europe's most endangered mammal, the Mediterranean monk seal.

But intensive tourism has exposed the seal to pollution, untreated sewage and industrial waste.