Thames Water, the UK's largest supplier of water, has been fined a record £20.3 million after admitting it pumped more than a billion litres of untreated sewage into the River Thames.
The company was prosecuted by the Environment Agency and sentenced at Aylesbury crown court on Wednesday.
The judge, Francis Sheridan, described the case as a "shocking and disgraceful state of affairs”.
“It should not be cheaper to offend than to take appropriate precautions,” he added.
In a statement Thames Water said it "deeply regrets" the incidents, which occurred in Buckinghamshire and Oxfordshire in 2013 and 2014, and saw more than a billion litres of untreated sewage leak into the Thames and its tributaries, killing fish and wildlife.
There were also reports of nappies and other sewage debris spilling into the river.
The company's CEO, Steve Robertson, said in a statement it was "clear that our performance in this part of our region, at that time, was not up to the very high standards that we and our customers expect".
Thames Water said it had since reviewed its operations and made a number of "key changes" to "improve reliability". Its performance had since "significantly improved", Robertson added.
The six facilities involved were five sewage treatment works in Aylesbury, Didcot, Henley, Little Marlow, and Arborfield, and Littlemore sewage pumping station.
The company said it would add £1.5 million to pay for projects to improve the river, its wildlife, and the surrounding environment at the affected locations.