The dolphin was spotted in the Foyle

Fisheries officers in Londonderry believe it had become separated from its mother.

It was spotted and photographed near St Johnston in County Donegal at the weekend.

The mammal had swum up the Foyle and was visible in the river, about 10 miles upstream from the city centre.

It is believed to be the first dolphin to show up in the Foyle.

Lionel Nobbs from the Loughs Agency was one of those who saw it close up.

"Myself and a colleague launched a boat and went across to where the dolphin was spotted," he says.

My first concern was whether this was a rescue mission, but at no time did I think the dolphin was in any danger Lionel Nobbs Loughs Agency

"It was clearly visible and we stayed with the dolphin for about an hour.

"It was just over a metre long, and a farmer who lives nearby said he saw it eating a silver-coloured fish that morning.

Mr Nobbs says that on the day the dolphin arrived, a large number of migratory fish were in the river.

"I'm convinced the dolphin was eating fish - there was an awful lot of fish seen around the dolphin, including salmon and trout."

Although the dolphin was out of its normal habitat, Mr Nobbs says there was no need to help it out.

"My first concern was whether this was a rescue mission, but at no time did I think the dolphin was in any danger," he says.

"It didn't appear to be stranded at any time. It was moving about quite freely."

Mr Nobbs says it was a wonderful experience to see the dolphin at such close quarters, but he is convinced it has now returned to the sea.

The dolphin was not the first unlikely visitor to the river - several years ago, a whale was also spotted there.