Quebec’s Ministry of Environment says a hydroelectric dam on the Lièvre River is responsible for thousands of dead fish.

Ministry officials say an over-saturation in gas in the water at the Brookfield Hydroelectric Dam was killing the fish.

“It’s a phenomenon when there’s too much air too much gas in the water,” said Michel Rousseau, Quebec’s assistant deputy minister of environment.

“When a fish comes in contact with this, it can die rapidly”

Rousseau said the water became too saturated with tiny air bubbles in a phenomenon called supersaturated dissolved gas. The fish then die from gas bubbles disease, or a “gaseous embolism”.

The first of the dead fish began to wash ashore in early July. At the time, Quebec government officials said the analysis revealed the fish died of “acute intoxication”, likely a toxic spill, but could not identify the cause.

“There’s no spill,” said Rousseau.

“There’s no toxic element in the water.”

The Minister of Environment has ordered the dam, which is located in Masson-Angers in Gatineau, to bring in an expert to identify the operating conditions of the dam that is resulting in the dead fish, as well as monitor the dissolved gas levels in finding a fix to the issue.

The vice-president of public affairs and sustainability for Evolugen appeared to attribute the high gas levels to this spring’s flooding, saying in a statement to CTV News:

"This spring's extraordinary flooding and high water flows caused unusually high levels of debris in the Lièvre River which has resulted in more frequent clearing of debris than the norm at our facility," Vanessa Pilotte wrote.

“Our investigation is ongoing and we continue to collaborate with all government officials.We operate to the highest standards globally and comply with all laws in the jurisdictions in which we operate. This is an unprecedented event not seen in our decades of operations.”

The Minister of Environment has ordered the dam, which is located in Masson-Angers in Gatineau, to bring in an expert to identify the operating conditions of the dam that is resulting in the dead fish, as well as monitor the dissolved gas levels in finding a fix to the issue.

When CTV News asked if Brookfield Renewable Canada could face fines, Rousseau did not rule it out, saying it’s possible once the investigation is complete, but it’s still ongoing.