Toronto's animal services agency is investigating after 30 ducks and one heron were found dead on the sandy shores of Woodbine Beach Sunday morning.

Parks Toronto initially told CBC Toronto approximately 50 ducks were found dead, but later said there were in fact 30.

Joanne Ingrassia, a volunteer with Toronto Wildlife Centre, told CBC Toronto she came to the waterfront hoping to rescue any birds that were still alive.

"Sadly it doesn't look like any have survived," she said, adding that many lifeless birds in various stages of decay in the water are still washing up.

Crews from Toronto's Parks, Forestry and Recreation were at the beach cleaning up the ducks' bodies throughout the day for the city's animal services agency to conduct an investigation.

"All have been removed," said Toronto Parks, Forestry and Recreation spokesperson John Bugailiskis in an email.

"A necropsy will be done on the animals to determine cause of death."

The dead ducks are not all one breed. Ingrassia said she saw different types of arctic ducks and long-tailed ducks on the sand.

Toronto Animal Services are probing what caused the ducks' death. (Keith Burgess/CBC)

Toronto Animal Services hasn't identified the cause, but Ingrassia believes bacteria in Lake Ontario could have been the cause.

"It's hard to say what caused it but we suspect it's possible that it's botulism," she said. Avian botulism is a paralytic disease found in waterfowl that is fatal and causes paralysis.

"I'm not aware of this happening here before," she added, noting she has lived in the Beach neighbourhood for more than 30 years. "I have seen botulism in waterfowl before but not this many at one time."

Toronto Animal Services say they are working to pinpoint what caused the ducks' death.

In the meantime, Bugailiskis is advising dog owners to ensure they are kept leashed in the area.

"If the dog was in the park today and has developed any symptoms of illness, they should take their dog to their veterinarian," he said.