Salmon do U-turn in River Thames until sewers fixed

Twenty thousand juvenile salmon were released in a River Thames tributary outside London last year to see if they would migrate to sea and return home to breed. Only three came back.

Sewage spilling into the river that bisects Europe's financial capital may be the reason, said Darryl Clifton-Dey, head of a programme to reintroduce the migratory fish to the Thames after a 176-year absence. Sewer owner Thames Water Ltd estimates 32 million cubic metres of waste flow into the river a year, enough to fill 12,800 Olympic-sized swimming pools.

"Sewage could be the straw that's breaking the camel's back," said Clifton-Dey, a scientist at the Environment Agency, the government watchdog for water quality.

"Because they need lots of clean water all the way along, salmon are a very good indicator species of the general health of the whole river."

With Victorian-era sewers failing to control overflows that occur about once a week, Thames Water plans a $3.2bn upgrade. Final bidders for the first $648m contract include Vinci SA, the world's largest builder, and Hochtief AG, Germany's biggest, with work to begin in 2010.

Like New York's efforts to clean up the Hudson River, whose bass were contaminated by mercury, and attempts to revive the Huangpu River where Shanghai gets most of its drinking water, London is trying to restore an historic waterway whose health has suffered from population pressures and industrialisation.

Thames Water is owned by Kemble Water Holdings Ltd, itself owned by an investor group led by Australia's largest investment bank, Macquarie Group Ltd. The utility is planning two tunnels to collect overflow from the capital's original sewers. Builders will dig as far as 75 metres under London, deeper than any of the city's subway lines.

The first tunnel will stretch for 7km, passing under the River Lee, a tributary of the Thames, to channel overflow to the utility's Beckton sewage treatment plant in East London. The Lee winds through the site of the 2012 Olympic Games and into the Thames east of Canary Wharf, home to the city's second financial district and skyscrapers housing offices for banks including Barclays Plc and HSBC Holdings Plc.

Further east at Woolwich, the city's main flood defence, the Thames Barrier, stretches a third of a mile across the river with 10 steel gates that can be raised to protect London from tidal surges such as the 1953 floods, when water lapped the top of the walls defending Parliament and about 300 people were killed along England's east coast.

Rod Kirwan, a London lawyer, rowed on the Lee, also called the Lea, for four years and said its course through fields in east London meant it could be "quite leafy and lovely." It could also be an unpleasant experience on certain days.

 "After heavy rainfall, there were stretches of the river that stank and gas was bubbling up," said Kirwan, a partner at the London law firm Denton Wilde Sapte. "If you close your eyes, you had no idea you were in central London. Yet in the water it was definitely urban reality."

Thames Water, formerly owned by Germany's RWE AG, aims to pick a builder for the Lee tunnel as early as November, said Nick Tennant, a spokesman for the Tideway Tunnels unit. "It's a massive project, set to be the biggest contract that Thames Water has ever let."

Overflows into the Thames and its tributaries happen about once weekly. Officials say they're triggered by as little as 2mm of rain that washes down drains to the sewers, which spill over into the river because they were designed when London had less sewage and more unpaved areas to absorb rainwater. In the Thames, bacteria break down excrement, using up the water's oxygen and stifling fish.

Plastic bags, prophylactics, sanitary napkins, tampons and Q-tips blight the waterway and river shores, said Chris Coode, river programmes manager for the litter-cleanup charity Thames 21.

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