Thames Water has been fined £2.3 million for a pollution incident in 2016 that allegedly resulted in the death of more than 1,100 fish.
The incident involved a leak of untreated sewage with a high ammonia content into the Dawley Court ditch and stream that flows into the River Thames.
The water company was also ordered to pay the Environment Agency’s costs of £87,944.
Aylesbury Crown Court Judge Francis Sheridan said the company’s breach of environmental standards constituted high negligence.
Sarah Bentley, Thames Water Chief Executive Officer, who joined the company in September 2020, said: “We’re really sorry for what happened in Henley five years ago. Discharges of untreated sewage are simply unacceptable and we will work with the government, Ofwat and the Environment Agency to accelerate work to stop them being necessary.
“Our business plan for the next five years includes an unprecedented amount of investment, much of it directed towards safeguarding the environment. We have a long way to go and we certainly can’t do it on our own but the ambition is clear.
“My aim will always be to try and do the right thing for our rivers and for the communities who love and value them. I am passionate that we set out stretching targets and learn from past mistakes like this.
“There is still a lot to clean up from the past and also a great deal to invest in the future with today a brilliant example of both.”
An Environment Agency spokesman said: “This £2.3 million fine for Thames Water for an entirely foreseeable pollution incident in 2016 laid bare the company’s management failings.
“Protecting England’s rivers and lakes is one of the Environment Agency’s top priorities. Our enforcement action over several years has led to improvements in how water companies operate, but the damage caused to the environment at Henley shows water companies have a lot more to do.
“Sitting at Aylesbury Crown Court today, Judge Francis Sheridan said a number of equipment faults at Thames Water’s local sewage treatment plant should have been identified and fixed ‘long before’ the company reacted.
“More than 1,100 fish died after untreated sewage was released into a local stream.”