A farming couple who say they had 21 sheep killed by dogs have called for the animals responsible to be put down.
Meirion and Ruth Cordiner, from Llanferres, Flintshire, say another 15 sheep were injured, and they expect to lose more through shock and infection.
They claim two dogs were captured by police and a dog warden, but were returned to their owners.
North Wales Police are investigating the incident, which happened on land the couple farm at Bradley, Wrexham.
The Cordiners, who had a 245-strong flock in Bradley, discovered the extent of the slaughter when they received a telephone call last week from someone who had spotted blood on sheep.
She added: "We literately found a dead sheep every 30 ft in the river."
As they were collecting the bodies, Mrs Cordiner said a man shouted for help nearby because two dogs were trying to get into his deer enclosure.
With the help of a police officer, the dogs were later cornered and collected by a dog warden.
The couple expected the dogs to be put down, but Mrs Cordiner said they were told by a council warden there was insufficient evidence, and the dogs, which had identity chips, had been returned to their owner.
She said: "The dogs may not have had signs of blood on their coats and mouths because the dead sheep were in the river so all evidence could easily have been washed off".
Mrs Cordiner said it was impossible to say how much money the incident had cost them, because they fear they could lose more sheep, and some animals are still unaccounted for.
She added: "The most important thing is to get these dogs taken off the owners before any more sheep become victims over the next few months.
"These dogs are pack animals and have had a taste of blood and will kill again.
"We have plenty of support and will do our best to get these dogs impounded once the police have collected all the evidence."
Wrexham council has been asked to comment.