A MENU from 1466 gives some idea of the size and biodiversity of the great lost fens.

The feast for the enthronement of George Neville as Archbishop of York featured thousands of wetland birds, including 400 swans, 5,000 geese and 4,000 ducks. It also included 200 'bytternes' and 1,000 'egritts'.

More than 500 years later, once-plentiful bitterns and egrets are incredibly rare - victims not of hunting but of loss of habitat, according to Dr Ian Rotherham, of Sheffield Hallam University,.

His research shows the marshes on the flat land east of the Pennines were vast, smaller only than the Cambridgeshire Fens and Somerset Levels.

From Lincolnshire to York and from Doncaster to Beverley, the landscape comprised tracts of water, bogs and marshes interspersed with areas of woodland, or 'carrs', and islands on higher ground.

The Isle of Axholme near Doncaster was just that.

Dr Rotherham, of the Tourism and Environmental Change Research Unit at Sheffield Hallam, says people are stunned when they realise what has been lost.

"People are gobsmacked. They know the area, but they have no knowledge of that fantastic landscape existing.

"For someone like me, it is absolutely heart rending. It was an almost unbelievable extinction of species that is beyond anything we can comprehend."

Today, only one per cent of the original area remains, at Thorne Moor, near Doncaster.

Dr Rotherham added: "Thorne Moor is the second-richest area in Britain, in terms of animals. If that was the same at the lost fens elsewhere, there would have been an incredible wealth of animal and plant life.

"It's terribly sad and one of my passions is to reawaken the memory of what we had.

"People don't understand the scale of change and the implications of the loss - but it's having very serious consequences today."

Drainage of the fens began in the 17th century, with a law for the 'recovery of drowned grounds', and gathered pace as technology improved. Dutch experts were superseded by Victorian mechanisation. During the Second World War, more land was drained to grow food and this 'improvement' continued right up until the end of the last century. Meanwhile, demand for peat as fuel and animal bedding steadily increased over the centuries.

At the same time, the Pennine moorland to the west of Sheffield was also being drained, channelled and built over. Places names like The Moor and Crookesmoor in Sheffield recall a much wetter and wilder landscape.

These vast bogs - up and downstream of the urban areas - acted like a sponge soaking up water.