Thames Water has been fined £3.3m after it discharged millions of litres of undiluted sewage into two rivers, killing more than 1,400 fish.
There was a “significant and lengthy” release of sewage from treatment works near Gatwick Airport in October 2017 into the Gatwick Stream in Sussex and River Mole in Surrey, a court heard.
Thames Water admitted four charges in an Environment Agency prosecution.
It was handed the fine during sentencing at Lewes Crown Court.
The company, which serves 15 million households, faces concerns over its future amid mounting