Thames Water has been fined £4million for allowing sewage to pour into two Oxfordshire streams - killing thousands of fish.
Its failure to maintain a sewer led to an estimated half-a-million litres of raw sewage being discharged into the streams.
The pollution led to the deaths of 3,000 fish in the Seacourt and Hinksey streams.
The water company was fined five years after the incident, in a sentencing hearing on Friday.
A sentencing judge labelled the pollution a disgraceful state of affairs in an area of outstanding natural beauty.
However, campaigners say the sentence did not go far enough.
Campaigner Sarah Webb and Councillor Ag MacKeith, from Hinksey Parish Council
Thames Water says it is working as hard as it can to stop any discharges of untreated sewage into waterways following its sentencing over the July 2016 incident.
It had previously been fined £2.3 million after another Oxfordshire waterway was polluted by sewage.
Sewage with high levels of ammonia was released into Fawley Court Ditch at Henley-on-Thames in 2016, killing 1,144 fish and other water life.
A court heard a failure to address equipment faults at a sewage-treatment plant in Oxfordshire made the incident “entirely foreseeable”.
Richard Aylard, Sustainability Director, Thames Water
After that incident, poor management at the plant was laid bare at Aylesbury Crown Court.
It emerged Thames Water’s treatment works at Henley had no adequate monitoring in place to manage the risk of pollution, and staff had not responded to alarms highlighting faults in the process.
Thames Water appointed a new CEO last year, who vowed to improve maintenance across the company to avoid a repeat of the sewage incident.