Environmental campaigners slammed the departing boss of Thames Water for "reaping big bonuses" while criminally allowing the company to dump sewage in Oxfordshire's waterways.

Sarah Bentley has unexpectedly resigned as CEO of the water company with immediate effect.

According to the company's own map of discharges, a Witney stream had almost four days of sewage dumped into it over a week in January, making it the worst in the Thames Water region.

Hardwick Brook, in the Rushy Common Nature Reserve, topped a list of rivers for hours of sewage pollution spilled.

The spills, which are usually justified by companies when sewage networks and works are overwhelmed by heavy rainfall, came despite only 3mm of rain over the period.

Stewkley, a sewage works near by, spilled for longer than any other Thames Water works.

Witney-based Ash Smith, chair of Windrush Against Sewage Pollution (WASP) said: "When Sarah Bentley arrived in the job I asked her what she thought about Thames Water breaking the law. She told me that the important thing was to do what was right for our rivers.

READ MORE: Oxfordshire school closes due to Thames Water supply issues

"Then she told us untreated sewage pollution was unacceptable but still made us accept it. 

"The company never stopped breaking the law and it remains part of normal business propped up by Government non-prosecution policy and failed regulators."

He added: "Now, in common with a trail of CEOs that have led the law-breaking company and reaped big bonuses while doing so, she has left.

"And it looks like her replacement will be a former CEO of Ofwat - yes, an ex-CEO of the organisation that should have prevented the scam is now going to benefit from it.

"How much longer will our government subject us to being the captive victims of a  voraciously parasitic business instead of taking it back to public, nonprofit ownership?"