A three-year-old Cavalier King Charles Spaniel has died after being poisoned along the Comber Greenway.
It is understood the little dog was left in a critical condition after consuming rat poison, which was left along the popular pathway where dog walkers regularly take their pets, on Wednesday night.
Siblings Lily and Darcey, owned by a mother and daughter, were out for a walk along the Greenway when Lily ate the poison.
Yesterday she was undergoing emergency medical treatment at a veterinary surgery. However, on Friday morning her owners confirmed she had passed away.
Jo Crossley, who runs Dog Friendly NI, said owners are running a gauntlet every time they take their pets for a walk along public footpaths.
"I really don't know what's wrong with people," she said.
"It's crazy to think someone would be so cruel to do this sort of thing to someone's pet.
"This is just the latest in a series of incidents we've seen in recent days."
Last week a plastic container with pills covered in gravy was spotted along the Comber Greenway, and anti-freeze was left out in a water bowl in Comber.
Jo added: "There's no evidence to say who is doing this and there is nothing in legislation to protect dogs. The consequences can be horrific, especially for people whose dogs may be their only real friend.
"Anyone out walking their dog needs to be extremely vigilant. And if you suspect your pet has eaten something it shouldn't have, please go to your vet as soon as possible."
Lily is owned by a close friend of Jo's.
"The perpetrators need to be caught and this campaign of hatred towards dogs has to stop, and in particular in this part of Belfast. No family should be put through this anguish," she said.
Gareth Wright, who runs the Comber Greenway Campaign, said this is not the first time that incidents threatening dogs along the Greenway have been reported.
"We do seem to get strings of these attacks, particularly at this time of year," he said.
"This time last year we had similar incidents, with poison being left along the path, even razor blades placed in jelly.
"It's disturbing and something I have alerted police to, but without evidence, there isn't much they seem to be able to do.
"It's an all too familiar pattern along the Greenway.
"It was also disturbing to see the warning 'Dog walkers beware' spray-painted across one of the bridges along the Greenway earlier this year."
Mr Wright said the consequences could be very serious, adding: "This seems to be the work of a lunatic.
"Not only is this sort of act a danger to pets, it's a danger to wildlife. And worse still, what happens if a child picks something up? It's that serious."