SEWAGE has polluted part of the Hughenden Manor estate land, after a cover is thought to have been removed by Thames Water.
The National Trust, which runs the Manor and park, has been working with Thames Water and the Environment Agency to try to resolve the water contamination issues.
Jim Foy, NT general manager, for Hughenden, West Wycombe and Central Chilterns Properties, said: "On Friday, February 14 Thames Water opened the foul sewer cover in Hughenden’s historic parkland in an attempt to relieve pressure on the section in the Hughenden Valley Road. This caused effluent to escape, polluting the surrounding area, not just in the parkland but also the chalk stream three metres away."
He said the EA has been told about the potential risks to water courses, grazing animals and visitors.
He added: "In an attempt to mitigate any of these impacts we have erected temporary fencing around the foul sewer cover and erected temporary signs, warning visitors and local walkers of the potential risks. We have escalated the matter to Thames Water yet remain concerned that to date it is unresolved and are eager to see a swift and permanent solution."
Spokesman for Thames Water, Sarah Sharpe, said: "Wastewater coming out of the sewer network is heavily diluted with groundwater, and therefore poses minimal risk. We are monitoring the watercourse and will continue to work closely with the Environment Agency."