A leading archaeologist has warned that illegal climbers are damaging Silbury Hill.
Heavy rain has led to standing water around the monument and the sodden ground is being eroded by trespassers climbing the hill.
Access to the man-made mound, which dates back to 2400 BC, has been prohibited for a number of decades.
Jim Leary, an archaeologist for English Heritage, said: "I would really ask people not to go up the hill. It is leaving some really rather hideous scars and eroding our beautiful monument.
"They are going up and it is very wet and they are eroding the side of the hill."
The hill is almost completely cut off by a moat with surrounding fields also underwater due to the recent heavy rain.
However, Mr Leary said that as far as the monument was concerned the flood water was nothing to worry about.
He said: "It is not a very common phenomenon but it has happened before in 2007 when it was very wet, and also in 2000.
"The mound has been there for 4,500 years and I'm sure it will continue to stand despite the weather."