This article originally appeared on VICE.

The scale is hard to imagine: gray sludge, several feet deep, gushing with the force of a fire hose through streams and forest—coating everything in its path with ashy gunk. What happened on Monday might have been one of North America’s worst environmental disasters in decades, yet the news barely made it past the Canadian border.

Last Monday, a dam holding waste from the Mount Polley gold and copper mine in the remote Cariboo region of British Columbia broke, spilling 2.6 billion gallons of potentially toxic liquid and 1.3 billion gallons of definitely toxic sludge out into pristine lakes and streams. That’s about 6,000 Olympic-sized swimming pools of water and waste containing things like arsenic, mercury, and sulphur. Those substances are now mixed into the water that 300 people rely on for tap, hundreds from First Nations tribes rely on for hunting and fishing, and many others rely on for the tourism business.

“It’s an environmental disaster. It’s huge,” said Chief Ann Louie of the Williams Lake Indian Band, whose members live in the Cariboo region and use the land for hunting and fishing. “The spill has gone down Hazeltine Creek, which was 1.5 meters wide and is 150 meters wide... The damage done to that area, it’ll never come back. This will affect our First Nations for years and years.”

The waste came from a “tailings pond,” an open-air pit that mines use to store the leftovers of mining things like gold, copper, and, perhaps most notably in Canada, the tar sands—the oil-laden bitumen composites that have made the Keystone XL Pipeline so controversial.

The term “pond” can be a little misleading, as the structures can grow to the size of Central Park.

As Canada’s industry-friendly government has sold off hundreds of square miles of forest for mining over the past few years, toxic tailings ponds have become a regular feature of once-pristine Northern Canadian landscapes.

Environmentalists say they’re disasters in the making, and they say the Mount Polley spill is proof. While this week’s incident was notable for its size, Canadian environmentalists and indigenous activists say it may be a sign of things to come for the country, and perhaps the rest of the world as well, as mining for everything from rare earth metals to coal increases globally.

“Any time you rely on a dyke to contain something, whether it’s water or tailings, it’s going to fail some day, sooner or later,” said Henry Vaux, a resource economist at the University of California Riverside. “To think they’re bullet-proof is to fool yourself.”

It’s too early to tell just how extensive the damage from the Mount Polley mine is, but environmentalists like Mining Watch Canada’s Ramsey Hart are calling it an “environmental catastrophe,” bigger than the country has seen in years.

The tailings pond contained up to 85,000 pounds of lead, 152 tons of copper, and about 1,000 pounds of mercury, among many other heavy metals and potentially toxic substances, according to a government report. Now, many of those metals may be sitting in lakes and rivers, including one that’s home to one of the biggest salmon populations in the world.

Brian Kynoch, the president of Imperial Metals, which owns the mine, tried to calm an angry crowd at a meeting near the disaster area on Tuesday by saying the water was likely safe. “I’d drink the water,” he said.

But those who live in the sparsely populated area near the mine aren’t taking his word for it. They say the area is now completely ruined for drinking water, hunting, and fishing.

“Our economy swims in the river and walks by the ground,” said Chief Bev Sellars of the Soda Creek First Nations Tribe. “There’s not any amount of money in the world that’s going to fix what’s happened.”

First Nations communities near the Polley mine say they’re devastated by the loss of the habitat, but some say they saw it coming.

A 2011 report commissioned by two First Nations tribes and funded by Imperial Metals found that the tailings pond was structurally deficient to hold as much waste and water as it did. In 2012, the British Columbia Ministry of the Environment found the Mount Polley mine had failed to report that the pond was holding more water than it was legally allowed to.

Photo by Dru Oja Jay, Dominon, via Flickr

“We had concerns specifically about the tailings ponds for years,” said Sellars. “I hate to say it, but it wasn’t a total surprise to us.”

The size of the Mount Polley mine breach may be unprecedented, but whether it’s gold and copper mining in British Columbia or tar-sands mining in Alberta, the environmental impact of the process has become a near-constant controversy in Canada under Prime Minister Stephen Harper’s Conservative Party government.

In 2006, his first year in office, Harper declared his intention to make the country an “energy superpower,” and he’s done just that: Canada is now the fifth-largest oil producer in the world, thanks mostly to tar-sands mining in Alberta.

More than 1,000 square miles of land, including rare boreal forest, have been turned over to energy companies to mine for tar sands (which are not actually made of tar but bitumen). The viscous, oil-rich sands are processed using a variety of toxic chemicals and the leftovers are put in tailings ponds, which currently take up about 70 square miles in Alberta.

The tar sands could grow to 50 times their current size if Harper’s government gets its way. If they did, the development would rival the state of Florida in size.

“Massive areas have essentially been transformed into an industrial sacrifice zone,” said Ramsey Hart.

While it’s relatively rare for a tailings pond to fully collapse like the Mount Polley one did, researchers say that tailings ponds near the tar sands also have the potential for environmental disaster—just a slower, less visually compelling one. Research from Canada’s environmental agency has shown that tailings ponds in the tar sands region have leached potentially deadly toxins into land and groundwater, and First Nations tribes and environmentalists have blamed those leaching chemicals from the tar sands on rare cancer clusters.

The issue extends far beyond Canada. There are an estimated 3,500 tailings ponds worldwide. And thanks to lax government regulation in the US, an estimated 39 percent of tailings-pond dam failures happen in the states — a rate higher than anywhere in the world.

Just six months ago, a pipe at a coal slurry pond in North Carolina opened, leaching 1.1 billion gallons of sludge into a river.

The problem in Canada, the US, and elsewhere is that no one knows exactly what to do with these ponds. Much of the sludge they contain is too toxic to remediate and let back into the environment. As of now, the plan is to just let them sit there and hope they don’t fail.

Many of the ponds will likely exist long after their corresponding mines close, and therefore long after the people who were financially responsible for them are nowhere to be found.

“There’s really no long-term plan for these tailings ponds, and that’s where the risk comes in,” said Hart. “These places might be there forever.”