Why are hundreds of dead fish floating in the Ausable River? An investigation is underway

Residents are concerned about the large number of dead fish found floating in the Ausable River in Port Franks, Ont., and are questioning the safety of the waterway used by boaters and swimmers.

The municipality of Lambton Shores said it was alerted to issue on Saturday, with reports that hundreds of fish of various species were turning up in the marina and along the banks of the river, which flows into Lake Huron. 

Marilyn Smith, whose house is on the river, said about a dozen fish were caught up on her dock Monday. She estimated nearly 150 were floating downstream.

"People are boating in that river, children are swimming [in it]. If the fish in that river are dead, what could happen to humans?" Smith said. "Somebody has to take action and get this to stop."

On Monday, marine experts with the Ministry of the Environment, Conservation and Parks and the Ausable Bayfield Conservation Authority were on the river collecting samples and doing testing. 

"The ministry has confirmed that there are dead fish in various locations," said spokesperson Gary Wheeler. 

"Based on how widespread the dead fish have been located, both in the Ausable River and along the shores of Lake Huron, the die-off is likely the result of naturally occurring conditions," he said, adding the investigation continues.

Mari Veliz, the conservation authority's healthy watershed manager, said a number of factors can contribute to fish kills, such as viruses infecting a particular species, air quality issues and recent heavy rainfalls mixed with hot weather.

"The last few weeks, it's been warm, but it's also been very rainy. When the ground gets saturated, there's no place for the water to stay on the land, so it runs off the landscape and extra water also causes erosion of the stream channels, causing more sediment," Veliz said. 

"So we have a situation where water's running off the landscape, bringing sediment, and it's also the great amount of water running to the channel causing more downstream erosion."

Stephen McAuley, the municipality's chief administrative officer (CAO), said Monday this is the first time dead fish have been reported to them.

"We've seen small examples of this in other years, but I don't think to this extent," he said. "Our marina kind of just sits at the edge of the river, so it's not like a traditional marina that would have a big basin. The reality is that most of these fish will eventually get washed down shore."

The problem seems to be making its way to beaches around Lake Huron, including in Grand Bend, where residents have also shared Facebook photos of large dead Sturgeons washing up on the beach.

Smith said she was in Sarnia over the weekend and heard news of dead fish being found on their beaches as well that she believes may be caused by the Ausable River's streams, which flow in the same direction.