Only the feasting birds are happy now

Halfway through a sultry afternoon and the Thames at Kew looks shallow enough to wade.

Only when the tide begins to turn and water begins to flood back up river do the first signs emerge that all is not well.

There is a sheen and cloudiness about the water and, once the flood gains pace, the first dead fish float by. They are mostly small - perch, dace and bream - but every few minutes something larger slides past with a glint of silver.

For Gerry Hastings on the deck of the Thames cruiser Kingwood it is a grim sight. He started fishing the river when he was eight and has worked the Thames for 46 years. Earlier in the afternoon he watched as dead roach and chub drifted under Kew Bridge.

"The odd one showed a slight sign of life but most of them had had it," he said.

He first knew the river when it was full of fish and then saw the Thames effectively die from pollution in the Fifties and Sixties. But it has been reborn over the last 15 years with salmon, seals and even a dolphin returning.

"You see herons and cormorants now the whole time and they would not be here if it wasn't for a good supply of fish," he said.

"Until this happened there was excellent fishing here. There was a huge carp caught under Kew Bridge just the other day."

He was on the river when it rained for three solid hours on Tuesday and knew there would be problems.

He remembers the summer storm when the grease and filth swept from the sewers beneath central London's restaurants was so thick in the river that the boat's generators shut down when filters became clogged with grease.

The fish of the Thames have effectively been suffocated by an influx of water with little oxygen in it.

Thames Water are trying to pump that oxygen back. The Thames Vitality and the Thames Bubbler, both equipped with apparatus for bubbling neat oxygen back into the river, have been chugging through the stretch from Richmond, through Isleworth and Kew down beyond Barnes Bridge.

Hydrogen peroxide was being tipped into the river to help it recover.

"It may sound dreadful stuff but once it hits the water it releases enormous quantities of oxygen with only more water as a by-product of the chemical reaction," said Robin Clarke, wastewater operations director for Thames Water. He said oxygen levels are now back up to 30 per cent of normal.

Meanwhile the herons and cormorants on the islands in the Thames are gorging themselves on the floating corpses. What happens when the supply runs out is anyone's guess.