Some disturbing images around the Ottawa River in the Rockland area over the last few days.

Hundreds of dead fish washing up along the shore of the river.

CTV News was contacted by several viewers about the fish washing ashore at the Rockland marina.

There is an investigation underway to determine the cause.

There are several different species. In some places the water is thick with fish carcasses.

The Ottawa River keeper alerted Ontario's Environment Ministry on Monday. The preliminary investigation found the source of the die-off is upstream, from the Lievre River in Quebec. Quebec officials have launched their own investigation, report fish deaths in Masson Angers.

Matt Pigeon, from Rockland says everywhere he looks in the area, there are dead fish. “Basically, there’s a bunch of dead fish, all over the shoreline. Varied species, mostly bottom feeders. They all look like they’ve been dead for a day or two.”

Ontario's Environment Ministry is investigating. "As a precaution, we are notifying the operating authorities of the downstream water treatment plants in Ontario and will continue to liaise with the Quebec environment officials." Ministry officials said in a statement.

"We’ve also reached out to the Ministry of Natural Resources and Forestry to assess whether the die-off is a natural event related to pollution or a spill."