The Ministry of Natural Resources is investigating after hundreds of birds and fish washed up on the shores of Georgian Bay near Wasaga Beach.
Police say that the wildlife is scattered along a nearly three-kilometre stretch north of Wasaga Beach.
"You just want to cry," resident Faye Ego told CTV Toronto.
Locals said they noticed some dead fish on the beach a few weeks ago and a few dead birds earlier in September.
"But now this is just multiplied," Ego said, adding that the situation is "absolutely devastating."
Ontario Provincial Police Const. Peter Leon said that the number of dead birds is estimated to be between 5,000 and 6,000.
Cindy Parkin, a resident of the area, said that answers are needed.
"I'd like to get it cleaned up and figure out what it is, too," Parkin said. "It's pretty scary."
Ministry of Natural Resources officials said that the deaths could be the result of botulism.
Botulism thrives in low oxygen environments often found in zebra mussel colonies.
The Ministry said that more testing needs to be done.
With files from The Canadian Press and a report from CTV Toronto's John Musselman
