Tens of thousands of dead fish and even birds are washing up on the shores of Lake Erie in Canada in a bizarre mass animal death mystery.

Over the weekend and throughout the week,thousands of fish and birds have washed up along a 25-mile stretch of Lake Erie's northern shore. The fish species include yellow perch, carp, sheepshead, catfish, big head buffalo and suckers. Experts are now wondering what could have caused so many deaths and whether or not this is a threat to humans.

"First thing that crossed my mind, is there any potential danger to humans from a health point of view? Secondly, as I got more and more into it, what's the cause of this sudden fish kill in the lake?" Rick Nicholls, Member of Provincial Parliament for the Progressive Conservative Party of Ontario told NewsNet5.

Experts are trying to determine the cause of the deaths.  Samples of the dead fish and birds were sent to a lab to be analyzed. The Ontario Ministries of the Environment in Canada has a few ideas of what may have caused this mass death.

One idea is inversion. This natural phenomenon occurs when cold water goes to the lake's surface. Cold water has low oxygen levels, so this event can suffocate the fish.

"Essentially it's a rolling over of the lake," Ontario Ministry of the Environment spokeswoman Kate Jordan told The Chatham Daily News. "Something - whether it be a storm, or cooler temperatures at night, or strong winds - triggers a temperature change in the lake."

Another factor may have been caused the deaths is a sewage spill.

"It (the water) was quite putrid really ... I had never experienced anything like this,"  Neville Knowles, of London, Ont. and cottager at Rondeau Provincial Park for more than 50 years told The Star.

Dr. David Colby, the Chatham-Kent medical officer of health, told The Windsor Star that a strong scent could be smelled before the fish started washing up  on Friday. "All kinds of people were woken out of a sound sleep by a stench and it was like a septic tank was backing up," Dr.Colby said.

The strong smell and the bodies of thousands of fish ruined the Labor Day weekend for residents and tourists.

Although inversion or a spill is expected, early tests show that there was nothing out of the ordinary in the water based on field measurements of temperature, pH and oxygen levels.

"Those tests didn't show anything unusual in terms of water chemistry," Jordan said. "We did not observe any spill or pollution impacting the lake."

This is not the first mass fish death recently. Earlier this month thousands of dead fish washed ashore along the Texas coast from the Colorado River to Galveston Island. It is believed that low oxygen levels caused those deaths.