Thames Water has admitted that sewage leaked into the River Thame after a machine failure at its plant in Aylesbury.
A major investigation by the Environment Agency is currently taking place into pollution in the river, which backs onto the sewage treatment works in Rabans Lane.
While the Environment Agency remained tight-lipped about the probe, Thames Water admitted to The Bucks Herald that a leak had occurred.
In a statement it said: “Earlier this year sewage went in to the River Thame from our treatment works at Aylesbury.
“This was caused by the failure of equipment that had become blocked.
“We worked very closely with the Environment Agency to monitor the river and fully investigate what had happened.
“The equipment issues have been completely resolved and the works are operating as normal.”
Cuddington resident Doug Kennedy, an expert in biology and ecology, contacted authorities last month about pollution in the river which he claims is having a damaging impact on wildlife.
He said: “I regularly monitor this stretch of river as a bit of a hobby.
“I noticed something wasn’t right after I came back from holiday towards the end of July.
“I noticed a lack of dragonflies on the river and I also found a large dead fish at Eyethrope.
“I passed my concerns on to Aylesbury Vale District Council who informed the Environment Agency.
“They then rang me to say they were investigating major problems and infringements at the sewage works and the gentleman added that enforcement was in the offing.”
Mr Kennedy said that a possible reason for the lack of dragonflies would have been the hot spell of weather over the summer.
But he added: “The dry weather could have caused an oxygen deficit however I have seen no improvement in the dragonflies numbers recently, whereas in recent years there have been good numbers of the species at the same point.
“I am appalled that such an environmental disaster for the locality could be allowed to happen.”
Environment Agency officer Robert Davis said: “We are currently investigating a number of pollution incidents on the River Thame, downstream of Aylesbury.
“As the investigation is ongoing, we are unable to comment further at this stage.”
An Environment Agency spokeswoman said given the ‘ongoing investigation and sensitivity of the case’ she could not answer specific questions put to her.
She added: “We simply can’t risk jeopardising any enforcement action that could come as a result of our investigations.”
The sewage works was recently blamed for terrible smells over Aylesbury, however Thames Water engineers said they could not find any specific problem with the plant.