Eels are making a comeback to the Fens, with more of the snake-like fish slithering their way up our rivers and drains than have been seen in years.

Officials say 'exceptional' numbers of elvers have been recorded at the St Germans Pumping Station, near King's Lynn.

The young eels - around three inches long and the thickness of a shoelace - have travelled thousands of miles from the Sargasso Sea, off Cuba, to spend their lives in Fenland waterways.

A special fish pass has been built at St Germans - Britain's biggest pumping station - on the Middle Level Drain, to help elvers ascend the sluices.

The first eels were seen using it this Spring. Some 10,000 were recorded during the first three days of April, while 50,000 were counted in the first three weeks of the month.

Cliff Carson, chief environmental officer with the Middle Level Commissioners, which manage the Middle Level drainage system, said: 'It's great to see a boom year for elvers after so many years when their numbers were less than 5pc of former totals returning to the UK.

'We hope this trend will continue. The St Germans Pumping Station elver pass will give excellent access for eels and elvers into the Middle Level rivers and drains that will benefit eel population recovery in the future.'

From St Germans eels can travel far inland along the network of drains and dykes whicch stretch across the Fens. Some are even believed to migrate overland on moonless nights, to reach landlocked waters.

Eels are omnivorous, eating everything from invertebrates to small fish and frogs. After spending around a decade in freshwater, by which time they can be as thick as your arm and weigh in excesss of 5lbs, the adults set off on their journey back to the Sargasso, where eels from around the world gather to breed.

In recent years, eel numbers have seen a steep decline. Some blame a parasite which attacks the creatures' swim bladder - the organ fish use to control their swimming depth.