If you went down to the Thames today you were sure of a big surprise.

This giant sculpture of a polar bear stranded on a block of ice floated 7.5 miles from Greenwich towards the centre of London to highlight the problem of melting ice caps. The bear was also promoting the launch of a new television channel dedicated to natural history.

A total of 15 artists spent two months constructing the 20ft by 20ft square structure, which was launched at 6:30am before travelling up the Thames, stopping besideTower Bridge and the Houses of Parliament. The structure weighing, 1.5 tonnes, was winched into place.

The event coincides with the Eden Channel's Fragile Earth series, presented by Sir David Attenborough.

Melting ice caps threaten the existence of polar bears as their habitat disappears. There will also be serious consequences for the two billion people who depend on glacial meltwater to feed rivers.

Sir David said: “The melting of the polar bears’ sea ice habitat is one of the most pressing environmental concerns of our time. I commend Eden for highlighting the issue; we need to do what we can to protect the world’s largest land carnivores from extinction.”

The polar bear will also be touring other cities, including Glasgow and Birmingham.

Adrian Wills, head of the Eden channel, claimed it would address issues like climate change in an informative and entertaining way: "The Earth is a fragile place and we were keen to launch with a message that would draw attention to the uncertain state of our finely balanced environment."

The Thames is accustomed to unusual visitors. In January 2006, a seven-tonne bottle-nosed whale became trapped in shallow water near Battersea Bridge. Crowds gathered as the British Divers Marine Life Rescue (BDMLR) attempted to save its life. But despite the team’s efforts to move it into deeper water, the whale died.

Other mammals which have strayed into The Thames include a family of Harbour Porpoises, which were spotted near Vauxhall Bridge in December 2004. Another bottle-nosed dolphin was discovered swimming past Tower Bridge and Blackfriars Bridge in 2001.

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