CASES of otters raiding garden ponds could become more common as population levels increase, experts believe.

Otters, which once almost disappeared from the UK, are now present in every Suffolk river and a vast number of the county’s streams after a major campaign to improve water quality and habitat.

Suffolk Wildlife Trust (SWT) bosses have said there has been an increase of positive sightings in the region, while mammal ecologist Paul Chanin said animal numbers have been going up steadily for 30 years.

Dr Chanin, who has previously advised the Environment Agency, said that the otter population was about half to two thirds of the way back to levels seen in the 1950s.

He added: “It’s been an on-going process. The otter was badly affected by pesticides through the 1950 and 1960s and other toxic chemicals that may have affected breeding. Once we started clearing those things up, the otter population started to recover throughout the UK.”

Dr Chanin said a survey of 3,000 sites in 1977-1979 suggested that otters were only present at 6% of locations. A survey of the same sites more recently found otters at more than 50%.

But he said the length of the recovery, which has taken half a century, has meant people have forgotten what it is like to have otters “everywhere”.

He added: “In the meantime, fish and fishing has increased in popularity. People have not thought about the consequence of keeping ottery food in places where it is easily got.

“People keeping fish don’t seem to recognise that they are concentrating fish in one area, so it is hardly surprising that otters are coming to take them.”

Otters have been blamed for eating £10,000 of fish from a pond in Thetford and are now regularly photographed in waterways nearby. Dr Chanin said: “I’ve had records of otters going into gardens and ponds for about 20 or 30 years - initially in the south west. But as they increase in other parts of the country, the same has applied. “Just as you wouldn’t leave your rabbit or guinea pig wandering around the garden in case a cat or fox get it, you also have to protect your fish.”

Penny Hemphill, water for wildlife advisor with SWT, said: “Otters are now widespread in all of our rivers, and all smaller ones. You’ll also find signs of them in smaller streams.”

Ms Hemphill said efforts made by conservation organisations, who have worked with landowners, water companies and the environment agency had contributed to the rise. She added that rivers would only support a certain number of the protected top predator but said it is possible they will look elsewhere for food. She added: “If otters are hungry they will search for food. But generally they are a riparian animal, they live along rivers, and that is where they will stay.”

The Otter Trust, run by Philip and Jeanne Wayre, reintroduced many otters to Suffolk from 1971.