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.

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