Lake inversion is the most likely killer of tens of thousands of dead fish that washed up on the shores of Lake Erie over Labor Day weekend as Canadian officials believe no chemical or toxic spill was responsible.

Kate Jordan, spokeswoman for Ontario's Ministry of the Environment, told AM980 that investigators did not find evidence that a chemical or toxic spill or pollution caused thousands of fish to turn up dead on the Canadian side of Lake Erie.

Lake inversion is a process where surface water temperature drops dramatically and gets replaced with a bottom layer of water, which has lower levels of oxygen, Jordan told the Canadian radio station. Investigators believe lake inversion, which occurs about every two years, is what caused the fish to die, according to AM980.

Officials took water samples from Lake Erie in their investigation of the dead fish, with the Ministry of the Environment expecting results back in a few days, the station reported.

Despite the ministry's theory, local residents were skeptical, with some believing the dead fish turning up on Lake Erie's shores were caused by a man-made environmental disaster.

"At this time of the year it is common to get lake turnover or lake inversion and you usually do get a few fish killed ... but this smell smelled like a sewer ... and on top of the water there was a brown kind of milky film that was at the water's edge," London, Ont., resident Neville Knowles told the Toronto Star.

The dead fish put a dent in the beach plans of tourists who planned to flock to Lake Erie over Labor Day weekend, as well as fishermen. The dead fish started appearing Saturday along a 25-mile swath of shore, according to News Channel 5 Cleveland.

Jordan said it's unclear who will foot the bill for the cleanup effort on Lake Erie.

"We are having discussions with Environment Canada, the health unit and natural resources about that now," she told the Star.