A tanker trailer full of dead fish is seen in the water near Duncan Bay, B.C. on Dec. 30, 2019. (Tavish Campbell)

Heavy waves are being blamed for sending a tank trailer full of dead fish plummeting into the water off the coast of Vancouver Island last weekend.

Fisheries and Oceans Canada said the trailer rolled off the deck of a landing craft – a vessel similar to a barge – early Saturday morning north of Campbell River "due to heavy wave action." 

Witnesses told CTV News they saw something leaking into the water after the accident.

"There's a hatch and a valve and it's indented," said James Lawson, a commercial diver from the area. "There was some fish matter settled and then occasionally it would spurt out a pink liquid that would diffuse into the surrounding water."

But the owner of the vessel, Coastal Seatrucking Ltd., and Fisheries and Oceans Canada have insisted the trailer remained intact.

In an email to CTV News, a spokesperson for the DFO said "there was no discharge of dead fish into the environment."

The fish came from Cypress Harbour, a fish farm owned by Cermaq Canada. Officials said the deaths were not caused by disease.

Bill Vaughn, owner of Coastal Seatrucking, said the contents of the trailer were being pumped out Tuesday so the trailer could be removed from the water.

Fish farms are responsible for making sure carcasses are securely transferred to land, and officials said they will be checking to make sure proper procedures were followed.

"DFO is looking into this incident to determine if any licence conditions have been breached," the department's spokesperson said.

The incident follows less than two weeks after some 21,000 non-native salmon escaped into B.C. waters from a fish farm owned by Mowi Canada West.