Arrival of dolphins and seals gives Father Thames a clean new image

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With its pungent sewers and overcrowded banks, the Thames was described by the Victorian magazine Punch as little more than a "foul sludge and foetid stream".

With its pungent sewers and overcrowded banks, the Thames was described by the Victorian magazine Punch as little more than a "foul sludge and foetid stream".

Nearly 200 years later, the river has long benefited from a modern drainage system, making it unrecognisable from its more aromatic past. But it is only now that it is reaping the rewards of its cleaner waters.

The Thames has recently been transformed into a des res for bottlenose dolphins, basking grey seals, pilot whales and seahorses, creatures which were previously unable to live in the river because of its dirty waters.

A team of marine scientists is embarking today on a mission to discover the biological wealth of the river, after hundreds of recorded sightings of unusual species.

The Zoological Society of London's dolphin watch will try to shed light on the activities of creatures in the river.

It is hoped that the study will boost the limited knowledge of the river's burgeoning population of dolphins as well as other creatures such as porpoises and seals, all of which are being sighted more often, according to the society.

The renewal of life in the Thames offers hope that efforts to clean the river over the past three decades are paying off.

It was the dawn of the industrial age 250 years ago that was responsible for turning the river from a thriving habitat into a stagnant, black waterway.

As the factories of the Industrial Revolution pumped poisons into the waters, a vast number of species were forced out. Among them was the seahorse. Until the past few years, it was only found in the warmer, cleaner waters of the Bay of Biscay, the Canary Islands and Africa. Now, however, it has made its way back to London.

The discovery of a seahorse in the estuary last month created a stir among marine scientists as it was the first to be found since 1976, when a far smaller specimen was spotted much closer to sea.

A long-finned pilot whale sparked interest in the wealth of marine life in the Thames when it was spotted off Southend-on-Sea five years ago,

More recently, river police observed a bottlenose dolphin swimming at Blackfriars Bridge in central London, one of only 300 believed to swim in British waters. Harbour porpoises, of which there are thought to be as many as 350,000, have also been unexpectedly sighted as far upstream as Waterloo.

A common seal has been seen sunning itself on the banks of Richmond while grey seals - among the rarest in the world - have also been sighted.

The burst of life in the Thames is compelling evidence of the self-renewing properties of nature. "These sightings are all indications that the Thames has become a much cleaner and healthier environment for wildlife," said a spokeswoman for English Nature.

"We're absolutely delighted that the Thames supports more wildlife than it did 30 years ago. The fact that there are 118 species of fish is a clear sign that huge improvements have taken place."

Marine scientists know little about what dolphins are doing in the river, what they eat and how long they stay before returning to the sea. Alison Shaw of the Zoological Society hopes the programme will answer some of those questions.

Among the areas on which the study will focus is the impact of humans on the dolphins, an impact which is likely to grow if tens of thousands of new homes and businesses are built, as planned, in Thames gateway development.

"Assessing the consequences of development activities requires long-term monitoring of these animals," Ms Shaw said. "To be useful, this must be put in place before new activities develop."

The Thames's tributaries are also improving. A fly-fisherman caught the first trout in London in more than 70 years last year in a section of the Wandle river next to Wandsworth council's bin lorry depot.

But with the celebration of a rich new selection of species comes the problem of dealing with their protection.

Scientists hope the new dolphin count will help to remedy this in part. While marine mammals are protected by UK law from capture or deliberate harm, it is difficult to enforce without knowledge of their numbers or behaviour patterns.

The need for enforcement was highlighted yesterday when a seal was found by the Thames near Gravesend, Kent, with 30 shotgun pellets in its head. The adult female has lost an eye and is in serious condition at the RSPCA's East Winch Centre in King's Lynn, according to Rob Mellow, the inspector who is investigating the attack. "Using a shotgun is nothing but cruel because it has not killed the seal, all it has done is cause it immense suffering," he said.