An investigation has been launched after hundreds of dead fish were discovered in an eastern Ontario river.

The fish have been found in recent days in the Ottawa River in Clarence-Rockland, Ont. Various species have been affected, including muskies, carp and catfish. Dead eels have also turned up.

"If you look out on the river, every white spot is a dead fish at this point," Eric Champagne, who often fishes in the river, told CTV News Ottawa.

"You could probably lose count, because there's so many."

Officials from the Ontario, Quebec and federal governments have all collected samples of the fish and water.

At this point, it's believed that the fish died in the Du Lievre River in western Quebec and then flowed downstream into the Ottawa River. Lack of oxygen is believed to be a key factor in the deaths.

"There's a wide variety of factors that could be causing that, because there's such a wide variety of species," said Patrick Nadeau, the executive director of watershed protection group Ottawa Riverkeeper.

Nadeau speculated that the lack of oxygen could have been caused by some sort of spill or leak into the river. Test results that could shed light on the mystery are expected to be available within days.

A spokesperson for Quebec's environment ministry told CTV News Ottawa that it was not aware of any spills in the river within its jurisdiction.

Clarence-Rockland announced Wednesday that testing had not showed any adverse effects on the local drinking water supply, although the water's temperature has changed.

Ottawa Riverkeeper is recommending that people not eat fish from the river until more information about the deaths is known.