Anglian Water has been named one of the worst performing water companies in the country.
The Environment Agency's annual report on the environmental performance of water companies rated Anglian Water two out of five stars for the second year running.
It said it was concerned the company "will not or cannot change" after causing over 250 sewage pollution incidents in 2022, with 11 of these defined as serious.
Anglian Water said it fully accepted it must improve, but added that it had made "drastic changes" over the last two years and that its region faces "unique challenges".
The Environment Agency said more than half of the serious sewage pollution incidents recorded last year were from the assets of Thames Water and Anglian Water.
It said that nationally, the 2022 results show "minimal sector improvement" and that most water companies are "not meeting basic environmental requirements."
In its report, the Environment Agency said: "We are concerned that some companies will not or cannot change.
"Anglian Water and Thames Water repeatedly dominate serious incident numbers.
"These water companies in particular need to make radical changes now, but all water companies have areas to improve.
"None can be complacent, and static performance is not good enough as we continue to tighten the EPA to ensure progress towards environmental expectations."
However, the agency did highlight Anglian Water's work with the Future Fens Integrated Adaptation Scheme as a good example of partnership to reduce flood risk to communities and enhance the environment.
An Anglian Water spokesperson said: "We take our responsibility to protect, restore and improve our region’s environment incredibly seriously and fully accept that our performance must improve.
"Over the last two years we’ve drastically changed how we operate to address more effectively the unique and complex challenges facing our region.
"This is detailed in our Pollution Incident Reduction Plan published on Wednesday.
"We know that we must do better on some critical measures of environmental performance, and we remain resolutely focused on continuing with this strategy at pace."
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