Harmful algal blooms have killed farmed Atlantic salmon caged in ocean feedlots north of Tofino, B.C., and a local environmental group documenting the aftermath estimates that thousands of fish were affected.

Cermaq, a Japanese firm headquartered in Norway, first reported the die-off on its B.C. farms on Nov. 15.

“Three of our farms — Binns Island, Bawden Point and Ross Pass — all located within our Tofino operating area, are experiencing harmful algae blooms which are affecting our fish,” reported David Kiemele, managing director for Cermaq Canada.

Kiemele identified the algal species as Chaetoceros concavicornis and C. convolutes. Clayoquot Action, a local environmental group, also confirmed the species with its own testing.

Even in low concentrations, these species can damage fish gill tissue, depress immune systems and provoke infections in various kinds of ocean life.

The Tyee asked Cermaq on Tuesday to confirm the number of fish killed by the bloom but Cermaq said it won’t release the numbers for “commercial reasons.”

Bonny Glambeck, campaign director of Clayoquot Action, said that members of her organization recently spotted divers at work and biowaste containers being loaded with dead fish at Cermaq’s Binns Island salmon farm near Ahousat.

A similar clean-up operation was observed at the adjacent Bawden Bay farm.

“They are still netting out dead fish at a tremendous rate and putting them into mort bins. The die-off is causing a tremendous amount of pollution in the ocean,” said Glambeck. As the dead fish decompose, their scales and body parts float around the ocean.

Water around the farms had turned from blue to “a dark brown muddy river-like colour,” she added.

Typically, each ocean-pen confined feeding operation contains about half a million Atlantic salmon and produces nitrogen- and phosphorus-rich sewage equivalent to a city the size of 180,000 people. The effluent contains feces and uneaten fish food.

The algal bloom die-off follows two years of sea lice plagues that Cermaq could not control with pesticides or mechanical de-licing equipment.

“Cermaq’s operations are caught in a vicious cycle of sea lice and die-offs, said Glambeck. “We’ll see if the [federal] Liberals keep their election promise to move this industry into onshore tanks by 2025.”

Harmful algal blooms, which have caused the farmed salmon industry billions of dollars in recent years, have expanded their range and frequency as climate change has warmed, acidified and robbed coastal waters of normal oxygen levels.

Increased agricultural pollution is also associated with the highly destructive blooms.

This spring, a massive algal bloom suffocated more than eight million farmed fish in northern Norway. Wild fish will avoid blooms, but caged fish can’t.

In a recent report to shareholders, the fish farm company Mowi (formerly Marine Harvest) acknowledged that harmful algal blooms, sea lice and disease killed nearly one million fish at 12 different Scottish facilities between July and September 2018.

The same report highlighted another Mowi die-off in Newfoundland. “There was a mortality incident with low oxygen levels due to high seawater temperatures which caused mortalities of 2.6 million fish with a biomass of approximately 5,000 tonnes,” it noted. The rotting fish could be smelled for miles.

As a result, the federal government temporarily suspended 10 Mowi licenses in Newfoundland.

But those are dwarfed by a massive outbreak that devastated corporate fish farms in southern Chile in 2016.

Two successive harmful algal bloom outbreaks killed 39 million caged Atlantic salmon, amounting to nearly $800 million in losses.

The Chilean blooms resulted in dramatic economic and social losses for artisanal fishermen as well as mussel and salmon farmers.

Researchers recently concluded “there is no scientific evidence that salmon farming is or is not affecting the frequency and extent of [harmful algal blooms] in Chile, because of major knowledge gaps and limited monitoring of environmental conditions. For example, there is no regular monitoring of areas without salmon farms that could serve as reference sites.”

A recent report from an anti-factory farming organization warned investors that global aquaculture “must overcome an array of environmental, social and governmental risks before it should be considered a sustainable solution to meeting the growing global demand for protein.”

The risks included climate change, algal blooms, infectious viruses, antibiotic use, fish feed dependence and lethal sea lice plagues.

Alexandra Morton, an independent biologist that has advocated for the removal of corporate fish farms from wild salmon migration routes for decades, said the B.C. events demonstrate the industry’s fragility.

“It is bloody November, and we are having algal blooms when it's cloudy and rainy season. That’s doesn’t bode well for this industry.”

Nature made salmon so they could move and go on incredible ocean journeys, said Morton.

“It doesn’t like having massive populations in one place swimming in their own feces. These fish weren’t made to do that.”