This is the third round of dead fish found in the river in recent weeks -- events the Ottawa Riverkeeper is calling 'not natural.'

Almost 1,000 dead fish have washed up on the shores of the Ottawa River this week -- the third round of killings recorded in July.

Like other kill-offs, this most recent round of dead fish were also found near the Lièvre River and included a number of species.

Larissa Holman with the Ottawa Riverkeeper says this big of a fish die-off is not natural.

"What the test results are saying, and what we're hearing from the authorities who are investigating this is that [the fish deaths are] most likely due to a contaminant that's being released into the river," she explains. "We don't believe [the contaminant] is something that's there all the time. It seems to be individual events that are being released and causing these fish deaths."

These cases are being investigated by both the Quebec and federal ministries of the environment. Holman says they are looking at which businesses along the river may be dumping into the river.

Anyone looking to swim along the Ottawa River should take precautions if they are in Masson-Anger.

Listen to the full conversation Holman had with Cormac MacSweeney on 1310 NEWS' Ottawa Today: