Environmental officials were dismayed after a company which polluted the river Wandle killing two tonnes of fish had its fine cut by £75,000. Thames Water will now be penalised just £50,000 for the “catastrophic” spill of industrial-strength bleach into the waterway at the Beddington sewage treatment works in September 2007.

The water company will now be penalised £50,000 for the “catastrophic” spill of industrial-strength bleach into the waterway at the Beddington sewage treatment works in September 2007.

Three judges at the High Court of Appeal today determined the £125,000 fine, issued at Croydon Crown Court in January last year, to be “manifestly excessive”.

But Dr Paul Leinster, Chief Executive of the Environment Agency, said: “The pollution caused by Thames Water in 2007 spread for nearly 5km of the River Wandle, and had a catastrophic impact on the local wildlife. This incident saw 20 years of careful river restoration work decimated in a matter of hours.”

“In serious pollution incidents such as this, we would like to see higher fines in addition to any action taken by the offending company, to provide a stronger deterrent to polluters.”

A mechanical fault at the sewage works allowed the chemical, similar to that used in swimming pools, to flow directly into the Wandle.

Several miles of the river had turned white within hours, dead fish were seen floating in the river, and two police officers sent to investigate found the smell of bleach so strong that they felt nauseous.

Theo Pike, Chairman of the Wandle trust said the reduced fine sent a weaker message to potential polluters, but stressed that Thames Water had invested £500,000 in restoration and environmental improvement projects immediately after the spill.

He said: “I’d rather that all polluters followed Thames Water’s lead by putting up their hands straight away and try to fix things on the ground straight away.”.

More than 7,000 fish were thought to have been killed as a result of the incident.