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Friday, 20 April, 2001, 17:08 GMT 18:08 UK
A tale of two rivers
By BBC News Online's Kamala Hayman
If you fell into the River Thames in the 1970s you would have to be rushed to hospital to have your stomach pumped.
The river was awash with untreated sewage.
Yet today, it boasts one of the cleanest urban estuaries in the world.
The 200-mile river begins in the Cotswolds and wends its way through such historic towns as Oxford and Abingdon before emptying into the estuary at Southend.
It passes through highly urbanised areas, which during the industrial revolution saw the build-up of factories and slaughterhouses.
During the Victorian era, both sewage and industrial waste spilled straight into the Thames.
It had once been a thriving salmon river, but by 1849 the fish had disappeared.
But the water continued to be used for public consumption and an estimated 35,000 Londoners died in a series of cholera epidemics.
It took until 1865 for a plan to be agreed.
Engineer Joseph Bazalgette masterminded a scheme of underground sewers to carry waste downstream to outfalls at Beckton and Crossness.
This improved the lot of central London, but seriously fouled the water downstream until a sewage treatment system was introduced nearly 20 years later.
All was still not well.
Increasing industrialisation and London's growing population in the early part of the 20th century continued to put a strain on the Thames.
A clean-up operation began in 1960.
Sewage treatment was improved, industrial discharges were removed, and biodegradable detergents became more widespread.
In 1974 the first salmon returned to the Thames.
Today the river supports 115 different species of fish and hundreds more invertebrates, plants and birds.
But keeping it clean remains an ongoing battle.
During heavy rain, London's sewage storm pipes overflow into the Thames, sending oxygen levels plummeting - particularly in the dry summer months.
Two vessels - the Thames Bubbler and the Thames Vitality - are deployed to replenish the river's oxygen levels.
Last year, the Environment Agency, together with Thames Water, the Office of Water Services, and the Environment Department, agreed a £1bn scheme to improve the capital's sewage works over five years.
The risk of flooding has been tackled with a £535m Thames Barrier, built at Woolwich in 1982, and a series of 36 smaller flood gates and barriers.
The River Severn - Britain's longest river - falls below the pollution standards of comparable rivers in Eastern Europe, says wildlife pressure group, the WWF.
It says the river is one of two in Britain needing "major restoration" to comply with new European Union legislation. The other is the River Trent.
In contrast with the Thames, much of the upper Severn runs through rural land bordered only by market towns, and remains largely untroubled by major industry or urban development.
It boasts some 67 "sites of special scientific interest" along its banks.
Leaving Wales, it eventually hits the more industrial and farming areas of Shrewsbury, Gloucester, and Worcester before reaching Bristol.
It suffers pollution from industry discharges, farm drainage and sewage works.
In 1999, the Environment Agency reported that pesticide pollution from farmland around Shropshire was a growing problem.
However, the agency argues that many problem areas have been tackled since the early 1990s.
Chris Witts, 56, was among those who once worked its barges.
He was just 16 when he began shipping petrol, living and working on board a barge, rarely returning home.
He skippered the last commercial grain barge along the Severn in 1998.
Now he is semi-retired and the author of several books about the Severn.
"The river is nothing like it used to be," he told BBC News Online.
"It was busy from 5am until 10 at night."
The regular movement of boats kept the river from silting up, but today the Severn must be routinely dredged to keep it navigable.
It remains a popular boating river - although now only for pleasure - and only the 42 miles from Stourport to Gloucester are passable.
Flooding is a major problem for the Severn, but not a new one.
The Romans were forced to build flood defences in Wales to protect their forts at Forden and Caersws.
The worst flood in its history was in 1795 when nearly all its bridges were washed away, including 16 in Shropshire alone.
Only last November, floods temporarily put more than 120 pumping stations and sewage and water treatment works out of action.
20 Apr 01 | Sci/Tech
UK's polluted rivers named
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