Tens of thousands of dead fish are showing up along the shores of Lake Erie, bringing with them a powerful stench and questions over what is behind the deaths.

“This is a very substantial fish kill and there’s something really wrong to have a fish die off like this,” Dr. David Colby, the Chatham-Kent medical officer of health, told the Windsor Star. (photo: Ontario Ministry of Environment) The Toronto Star reports that the dead fish were found over the weekend.

“There was a significant number of fish, tens of thousands,” Kate Jordan of Ontario’s environment ministry told the Toronto Star.

The Toronto Star adds that the 25-mile are of the dead fish along the lake’s Ontario shore extends “from west of the fishing village of Port Stanley in Elgin County to the village of Morpeth in Chatham-Kent or just east of Rondeau.”

“This is a very substantial fish kill and there’s something really wrong to have a fish die off like this,” Dr. David Colby, the Chatham-Kent medical officer of health, told the Windsor Star.

Nearby residents say the stench from the dead fish was overwhelming.

“All kinds of people were woken out of a sound sleep by a stench and it was like a septic tank was backing up,” Colby told the Windsor Star.

The cause for all the dead fish hasn’t been confirmed yet; some point to a natural phenomenon known as a lake inversion, which brings cold, less oxygenated water to the surface which causes fish to suffocate. But many think the cause lies elsewhere.

“At this time of the years 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,” Neville Knowles, cottager at Rondeau Provincial Park for more than 50 years, told the Toronto Star.

Colby, also skeptical of lake inversion being the cause, said he didn’t think there was a dramatic change in water temperature, and said that it also wouldn’t explain the sewage smell, unlike any he’s witnessed on the lake.

CTV Windsor has video: