Dolphins, Seals at Home in London's Reborn River

James Owen in London
for National Geographic News
April 22, 2005
Fifty years ago London's River Thames was so polluted that it was declared biologically dead. Now the river that flows through the heart of Europe's largest city is awash with wildlife—a triumph worth noting today, Earth Day 2005.

More than 130 seals have been spotted in the Thames since last August, according to the Zoological Society of London. Bottlenose dolphins have been seen upstream of London Bridge. And last summer the first sea horse was recorded in the Thames estuary in 30 years.

With 120 fish species, hundreds of thousands of birds, and a thriving fishing industry, the river now ranks among the cleanest metropolitan tideways in the world.

Ecologists say the Thames owes its revival to pollution control, which has vastly improved water quality.

Commercial fishers are among those reaping the benefits today, taking impressive hauls of eel, sea bass, and Dover sole, said Steven Colclough, a fisheries scientist with the U.K. government's Environment Agency. Colclough said the river is now the largest Dover sole fishery in England and Wales.

The fisheries scientist added that flounder, mullet, and smelt—now present throughout London—are being joined by fish that only tolerate waters untainted by pollution.

"Sea trout are coming back in ever increasing numbers," Colclough said. "Over [the] past four years, we have found sea lamprey spawning consistently in [west London], and the first river lamprey was recorded in 2002."

These incoming crowds are, in turn, boosting numbers of fish-eating birds, such as herons, kingfishers, and grebes.

In 1949 the eminent British ornithologist Richard Fitter declared that heron would never again breed in London. Yet today the number of heron colonies in the city are at an all-time high.

Heron Stronghold

"London has become a U.K stronghold for herons," said John Marchant, of the British Trust for Ornithology. "No doubt the birds are benefiting from a general improvement in water quality and fish stocks in the Thames."

The condition of the Thames—which rises and falls with the tides as far inland as London—was very different 150 years ago. 1858 saw the "Great Stink," when the stench of raw sewage got so bad Parliament, which meets in a riverside building, had to be dissolved.

In 1878 the pleasure steamship Princess Alice sunk in a river collision. Most of the 600 or so passengers who died did so because they were overpowered by a noxious cocktail of human and industrial filth before they could reach safety.

"By the 1950s the Thames was in an even worse state," said Martin Attrill, a marine biologist at the University of Plymouth, England. "A 20-kilometer [12-mile] stretch of river was completely devoid of oxygen."

After London's Natural History Museum declared the Thames biologically dead in 1957, work began to try to rehabilitate the river. Government measures improved sewage waste treatment and banned industry from discharging pollutants into the river.

Today more than half of London's sewage sludge is sold in pellet form as fertilizer for agricultural use.

Attrill says water quality has continued to improve since the 1970s. "There's been a clear and very dramatic decrease in levels of heavy metals and pesticides," he added.

And yet the Thames's ecological renaissance remains a well-kept secret, according to a survey commissioned by the Zoological Society of London (ZSL). Published last week, the survey found that 83 percent of Londoners thought dumped shopping carts were the objects most likely to be found in the river. Just 6 percent of respondents knew about the return of Dover sole. Only 7 percent thought seals could be seen.

"It seems that Londoners know more about tropical rain forests than the river on their doorstep," said Alison Shaw, aquatic conservation manager for the ZSL. "People can't believe there's anything in [the Thames], because it looks so brown and dirty. But that's just the nature of estuaries; they carry a large amount of sediments in the water column."

Eel Migration

Shaw hopes the ZSL can help the river shed its dirty old reputation through a project that will investigate how wildlife uses the Thames estuary.

For instance, researchers are currently tracking juvenile European eels on their spring migration upriver. The eels travel thousands of miles from the Atlantic Ocean's Sargasso Sea, where they are born. "The Thames estuary is also an internationally important area for migratory birds," Shaw added. "It's their first landing stage when they arrive in Britain. Large flocks feed on intertidal mudflats and grazing marshes."

She says it's important that Londoners are aware of the river's burgeoning biodiversity, not least because pollution threats remain.

During violent storms last summer, London's antiquated drainage system was inundated. Some 600,000 tons of raw sewage was released into the Thames to prevent the waste from flooding people's homes. As a result, many thousands of fish were killed.

The U.K. Government has so far stalled on plans for a 3.8-billion-dollar (U.S.), 22-mile (35-kilometer) tunnel under the riverbed to dispose of storm water and displaced sewage.

Perhaps the sight of dolphins surfacing opposite the Houses of Parliament will help swing the debate.

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