The RSPCA has described the way a dog was deliberately drowned in a flooded quarry as a "cold and calculating" act.

An investigation was launched after the decomposing body of a young dog was discovered on Friday tied inside a weighted down sack.

Around the neck of the animal was a metal lead that had been fastened to an Umbro rucksack. The rucksack, which was black with white piping, was filled with rocks.

The dog was spotted at Lafarge Quarry, Ferryhill Station, County Durham, by a member of the public when its body rose to the surface.

RSPCA inspector Graeme Foggin, who is leading the investigation, said he believed the dog, which was mostly ginger with a white chest, had been in the water for about a week.

He said: "I have no doubt that the dog was deliberately drowned and had been alive when it entered the water.

"Its condition was very poor, but when I examined it I could not see any signs of external injury."

He added: "Although it was quite a large dog it was young, so I'm assuming it was starting to get to the size and the age of being a nuisance, for want of a better word.

"Whoever had it has thought enough is enough and just got rid of it in a cold and calculating way."

The flooded quarry is a popular spot for anglers and it is hoped that someone may have seen what happened.

Mr Foggin said: "It is hard to imagine the kind of person who would do something like this.

"I would urge anybody who knows who owned the animal, or how it came to be in the water, to contact the RSPCA immediately."

Anyone with any information about the incident should contact the RSPCA on 08705 555999.