The incident, which occurred in October 2017, saw "millions of litres" of undiluted sewage pumped into the Gatwick Stream and River Mole, killing more than 1,000 fish.
The company had pleaded guilty to four charges related to illegally discharging waste.
The fine was imposed at Lewes Crown Court, with Judge Christine Laing KC stating that Thames Water had shown a "deliberate attempt" to mislead the Environment Agency over the incident.
The company has previously been fined £32.4m for pollution incidents in the Thames Valley and south-west London between 2017 and 2021.
Thames Water has apologized for the incident and has implemented new systems to prevent similar incidents from occurring.
LONDON DAILY ARCHIVE
Thames Water Fined £3.3m for Killing 1,000 Fish in Sewage Pollution Incident
Thames Water, a company that supplies water to one in four people in Britain, has been fined £3.3m for polluting rivers in West Sussex and Surrey.
04 July 2023 · 20:59 UTC
