The toxic stew of mine waste that spilled into Colorado waters and turned a river orange last week is three times as large as officials originally estimated.

The Environmental Protection Agency (EPA) on Sunday said it used better metrics to determine that agency regulators had mistakenly released 3 million gallons of wastewater laced with heavy metals, including lead and arsenic, into Cement Creek in San Juan County, where it made its way into the Animas River and then Colorado River.

Initial estimates put the spill at 1 million gallons of wastewater.

The toxic water moved so quickly downstream that it could not be contained, EPA officials said. However, the spill did not cause any “significant health effects” to animals, said EPA toxicologist Deborah McKean.

The Colorado Department of Parks and Wildlife conducted a test of the water’s danger shortly after the spill on Wednesday by submerging 108 fish overnight in the Animas River. Of those fish, the department said, only one died, according to The Durango Herald.

But last week’s spill was neither the first nor the worst to contaminate Colorado waters. In 1975, 100 miles of the Animas River "looked like aluminum paint," according to The High Country News, quoting The Durango Herald at the time.

Until the late 1970s, there were no regulations on mining in most of the region, meaning anyone could dig a hole anywhere and search for gold, silver, copper or zinc. Abandoned mines filled with groundwater and snowmelt, which became tainted with acids and heavy metals from mining veins and then trickled into the region's waterways.

Experts estimate there are 55,000 such abandoned mines from Colorado to Idaho to California, and federal and state authorities have struggled to clean them for decades. The federal government says 40 percent of the headwaters of Western waterways have been contaminated from mine runoff.