英语听力：自然百科 泰晤士河

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In 1858, the British Houses of Parliament were evacuated³ when the stench from the River Thames had become unbearable⁴. Untreated sewage had been leaking straight into the Thames. Victorian engineer Joseph Bazalgette remedied the situation by designing an extensive network of sewers⁵. However, a century later, the growing population has stretched it to the limit. The majority of the old system is still in use today. It's simply too expensive to replace it, and it's still causing big problems.

"And that's Western Pumping Station. It's part of the original Victorian sewage system for London. When the system is overloaded⁶ by rainfall, we have this problem again with overflowing⁷ sewage, and that pumping station can discharge up to about 50 thousand tons an hour with mixture of untreated sewage and urban run-off."

The sewage causes oxygen depletion⁸ in the river, killing⁹ fish and other marine¹⁰ life. Enter one of these vessels¹¹. This is the Vitality¹², and it can pump up to 30 tons of oxygen into the water in a day. The whole process of injecting river water with pure oxygen takes only a few minutes. The irony¹³ is that the only reason a system like this is necessary is because the Thames is now so much cleaner than it was even 50 years ago. Fish have returned. It's one of the most important fish nurseries in Britain with around 120 species.

"The Thames is fantastic asset. It's a flood defense¹⁴ mechanism¹⁵ and drains the whole basin. It supplies, for instance, 2/3 of London's drinking water. I really like it to be a busy, active river which is sort of appreciated and enjoyed by all types of people, yet one which is still renowned¹⁶ as being a haven¹⁷ for wildlife."

The regeneration of this river is a wonderful success story. But it will be a constant battle to keep it that way.

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