Sewage was pumped into the River Colne for 55 hours only a week after the latest volunteer efforts to help clean it.

The Maple Lodge sewage treatment works in Rickmansworth released overflow water from 1.15am on Sunday, February 18 until the early hours of Tuesday, according to a live map run by Thames Water. 

It warned sewage could therefore be in the waterway just days after locals waded through it as part of the 10-year 'Rediscovering the River Colne' scheme, which aims to change the perception that it is "dirty and unkempt".

Cllr Ian Stotesbury, who was among those volunteering, said: "Liberal Democrats have been making it clear in parliament as well as locally that the government must act to do more to bring water companies in line and do more to tackle the dreadful state of discharges and pollution in our rivers. 

“We need a properly resourced Environment Agency and the government to get serious - it took them two years to respond to calls to limit water company bonuses while rivers were being massively polluted, and they still don't seem to get the scale of the problem."

He added that projects like Rediscovering River Colne will only succeed with "action at every level".

"We need support not inaction from the government," he added.

Watford's Conservative MP, Dean Russell, said he was also concerned about pollution being discharged into waterways and wrote to Thames Water and the Environment Agency's chairman.

But he added: "Importantly, the government have improved storm overflow monitoring to 100% to understand the extent of this issue and to subsequently hold private water companies to account.

"I welcome the work the EA are doing with the regulator Ofwat to enforce accountability through the government’s Storm Overflows Discharge Plan.

"I have also expressed my support for the swift progress of the programme for Rediscovering the River Colne to the Environment Agency."

Thames Water, which owns the Maple Lodge facility, said it regarded all discharges as "unacceptable" and apologised to those affected.

A spokesperson said it had been impacted by higher long-term rainfall and "normal to exceptionally high" groundwater, but pointed to plans to upgrade over 250 sewage treatment works, including Maple Lodge, to reduce the need for overflows during wet weather.

The company said improving the health of rivers remains a "key focus" and added that it is the only company to provide live alerts for all untreated discharges.

An Environment Agency spokesperson said it was aware of permitted discharges into the River Colne and that these are designed to release excess water during heavy rain.

They added: “As a partner for the ‘Rediscovering the River Colne’, we are committed to playing our part in the restoration of the River Colne”.