The executive director of Lincoln County Human Society says the agency is reasonably certain a substance found Monday in a park popular with dog walkers was indeed rat poison - and that it was probably left to harm pets.

Kevin Strooband said the substance found in Alex Mackenzie Park, on Beech Street by Haig Bowl Arena, has not been chemically tested, but after consulting with pest-control experts the light blue pellets are most likely rat poison.

"I can't think of a good reason for someone to have put it there," said Strooband. "The only reason I can think of is malicious."

The humane society has removed the pellets from the park. Its officers have also surveyed the park and haven't found more poison, he said, adding they are stepping up patrols in the area.

"The reality is though, to leave that kind of poison on the ground only takes a few moments," he said. "So unless you have full-time surveillance of the park, you likely won't catch anyone."

Strooband said the humane society has not received any reports of sick pets as a result of rat poison in the park, but the agency continues to ask pet owners to be alert.

"It is a very popular park for dog owners," he said. "I know some owners let the pets run free in the park. And they really shouldn't. Not only is that against the bylaw, but you could also end up harming your pet."

There have been rumours of rat poison having been left in Linlake Park as well, but Strooband said there is no evidence of it.

On Sunday, Coun. Bruce Williamson posted on Twitter that four dogs in the neighbourhood around Linlake Park in the city's north end had died in recent weeks. He said the family pets suddenly got ill with similar symptoms, suffered seizures and died.

Strooband said the humane society has no information to confirm those deaths, or that they were caused by the ingestion of poison.

The humane society is asking anyone with information to call it at 905-682-0767.