A giant freshwater mussel found near Pershore is believed to be a regional record.

It was found by Peter Boulton at his Thornleigh Nursery, Drakes Broughton, who explained: "I was just checking the fishing lake and was surprised to see this large shell just on the water line. It was covered in grey clay and I was amazed at the colour inside after I had cleaned it up. I have never seen one as big as this before."

Naturalist Paul Whitehead said it was a Swan Mussel and although he had seen thousands dredged out of rivers, most of which when mature were only about 60 per cent of the size of the Drakes Broughton find.

"I have never seen one so large as this which is 195mm long and 125mm high," Mr Whitehead said. "I would imagine that this is probably a local or regional record."

He added: "We tend to forget that rivers are important for their biology and are not just there for the interests of people."

Mr Whitehead said he put the age of the mussel as no older than 26 years and probably about 20. He thought it might have been introduced by a bird into conditions near perfect for growth, with no predators and nourishment in the soil ideal.

"It raises some interesting questions, which are difficult to answer," Mr Whitehead said. "Such as, assuming it originated in the River Avon, is the Avon becoming a better habitat? Is this an example of a specimen that was particularly well adapted to conditions at a particular place in the river? Are there some places in the river which favour this species more than others? Was this specimen able to accept a spot in the river when competition for food resources was somewhat limited?"

Mr Boulton has given the mussel to the Almonry Museum and Heritage Centre in Evesham where, said manager Tony Whiting, it would be put on show. "I think it will create a lot of interest," he said.