The River Crane pollution that killed thousands of fish came from a damaged pipe leaking sewage sludge into the river, Thames Water confirmed.

Nature-lovers were shocked to discover the river poisoned on Friday morning, almost two years after a pollution incident nearly destroyed the Crane’s ecosystem.

Once again thousands of fish were killed and dog walkers reported the river turning black in places.

And Thames Water, which had invested £400,000 in restoration after accepting full responsibility in 2011, confirmed a damaged pipe between Mogden and Iver Heath caused the pollution this time.

A spokesman said: “A pipe that carries treated sewage sludge between our treatment works was damaged by an unknown third party last week.

“This damage caused liquid to flow out of the pipe, and was diverted into a surface water drain feeding the River Crane.

“We are hugely frustrated by this, especially after the work that has been done to restore the Crane following the pollution incident two years ago.

“We are helping the Environment Agency in its effort to establish who caused this pollution.”

Friends of the River Crane Environment (Force) advised dog walkers to keep their dogs out of the Crane’s water.

Trustee Frances Bennett said: “In 2011 we said this must never happen again to the River Crane, yet only two years later we appear to have another significant incident on our hands.

“There is obviously something very seriously wrong with the management of the river and its catchment.

“Force looks to the Environment Agency as the national regulator, to undertake a full investigation of the incident and put measures in place that will ensure that it never happens again.”

She said news of the incident unfolded as Force held a conference with the Environment Agency and Thames Water to celebrate the river and all the work that has taken place.

The Thames Angling Conservancy (TAC) described the pollution as a “devastating blow” to the river and called on criminal prosecutions for those responsible.

Chairman David Harvey said: “In the 21st century, how can it be that our rivers are still the default position for any outfalls – where is the protection they need?

“I am tired of seeing plans which will never deal with the real problem of outdated and antiquated infrastructure where we are living in the dark ages.

“We need action. We need criminal prosecutions that produce fines that are a real deterrent.”

Mr Harvey said he wanted answers as to whether the pollution leaked in as early as Wednesday, whether it was reported and how authorities responded.

Twitter users used the social networking website to post their concerns about public awareness of the pollution.

Chris Williams tweeted: “@LBRUT children paddling in raw sewage in River Crane Nature Reserve @w-end. EA warned LBUT [sic] council last wk so why NO warnings?”

- When did you notice the River Crane had become polluted? Let us know by using our comment facility below.