WILDLIFE experts say a harbour porpoise which died after becoming lost in the River Severn would have been searching for food.

The creature, which looks like a dolphin, was spotted on Sunday in an agitated state in Maisemore Weir after becoming stranded on its route up the river.

It later died but the Marine Conservation Society, which has headquarters in Ross-on-Wye, believes the mammal would have been chasing salmon into the shallows in the river when it became caught out by low tides.

Richard Harrington, from the Marine Conservation Society, said: "It is hard to know why the porpoise would have come into the shore but the most likely reason a porpoise would swim up the river is that it would be chasing prey.

"Once it came up the river it may have become disorientated and swam further up than it intended to.

"It probably got stranded and as the river got shallower it became beached so it couldn't move and its body would not have been supported by the water, which would have led to breathing difficulties and death.

"It is the most common cause of death for these animals when they become beached."

The Severn Area Rescue Association (Sara) tried to free the porpoise along with professionals trained in helping stranded animals. Their attempts to guide the stricken mammal to deeper waters failed.

Stuart Priday, from Sara, said: "We were called to the incident at around 1pm where the female harbour porpoise had come too far up the river and had got herself stranded.

"We sent a team out with specialist marine medics but by the time we got there it was on its last breath.

"If we had been called earlier there may have been something we could have done but it is quite important that if people see these animals and they are beached that they call us by ringing 999 and asking for the Coastguard.

"You can actually do more damage by putting it back in the water if it has been out for a while because it can drown."

It is the second time this year that a marine animal has become stranded in the Gloucestershire stretch of the River Severn.

In April, Sara was called to free two of the mammals after they had been caught near Berkeley Power Station.

On that occasion the dolphins escaped unharmed as Sara and the ebbing waters enabled them to be freed.