New Mexico has filed a lawsuit against Colorado in the nation’s highest court alleging the state should be held responsible for the Gold King Mine spill and its handling of the contaminants that have leached from surrounding mines for decades.

The lawsuit, announced Thursday and filed on behalf of New Mexico’s governor, environmental secretary and attorney general, alleges Colorado “is directly responsible” for the conditions that led to the disaster.

New Mexico officials say their 135-page bill of complaint in the lawsuit was filed Monday in the U.S. Supreme Court and that the action was taken after discussions and negotiations with Colorado officials failed.

“The Gold King Mine release is the result of two decades of disastrous environmental decision-making by Colorado, for which New Mexico and its citizens are now paying the price,” Attorney General Hector Balderas said in a statement Thursday.

For months, New Mexico has cried foul against Colorado and the Environmental Protection Agency, which caused the Gold King disaster in August, calling for someone to be held responsible. The lawsuit represents the most serious legal action taken against Colorado in the wake of the massive 3 million-gallon spill.

Colorado Attorney General Cynthia Coffman declined an interview with The Denver Post on Thursday but in a statement said the lawsuit was “unfortunate” considering the spill was the EPA’s fault.

“It’s unclear to me how suing Colorado furthers the states’ mutual goal of holding the EPA to its promise to ‘take full responsibility’ for turning our rivers yellow,” Coffman wrote. “An interstate lawsuit just gives the EPA another excuse to delay and does nothing for the environment or the citizens that have been impacted. It could take years, even decades, to resolve this costly litigation.”

Gov. John Hickenlooper said he was “disappointed” by the lawsuit but that it wouldn’t halt Colorado’s work to remediate leaching, abandoned mines throughout the state.

Coffman has said repeatedly that suing the EPA is an option Colorado could take if the agency does not respond appropriately to the disaster, which released 880,000 pounds of metals. About a week after the spill, Coffman met with her counterparts from New Mexico and Utah — including Balderas — at a summit in Durango where all three said they were weighing lawsuits against the EPA.

In the weeks that followed, Coffman said the group was in talks about moving forward. It was not clear Thursday how those discussions devolved into New Mexico’s legal attack.

Deputy New Mexico Attorney General Tania Maestas, one of the lead lawyers on the lawsuit, said Thursday that she couldn’t discuss what agreement her office was trying to reach with Colorado officials, citing a confidentiality agreement.

“We have come to the point where an action must be initiated so that we can move forward and not prejudice the citizens of New Mexico by inaction,” she said.

Maestas explained that the lawsuit does no foreclose on discussions with Colorado officials and that New Mexico hopes the legal action doesn’t sully the relationship between the two states. She said New Mexico would be open to a settlement.

The lawsuit contends that Colorado authorized the “risky strategy” of plugging mining tunnels with bulkheads — specifically in the Sunnyside Mine and American Tunnel surrounding the Gold King — to attempt to control acid mine wastewater drainage, which led to the disaster. Further, after the Gold King spill, Colorado officials downplayed the effects of the catastrophe.

“Colorado was fully aware of the enormous risks to downstream communities associated with their failed strategy of plugging drainage tunnels,” New Mexico’s chief environmental official, Ryan Flynn, said Thursday. “They essentially authorized the transformation of Colorado mines into an enormous wastewater storage facility, ready to burst. We’re fighting for New Mexicans to hold Colorado accountable for their short-sighted and reckless actions.”

The lawsuit says the Gold King’s contaminants wrought environmental and economic damage throughout the Animas and San Juan River riparian systems and severely strained New Mexico’s stressed water and economic resources.

“The Gold King Mine release was the coup de grâce of two decades of disastrous environmental decision-making by Colorado, for which New Mexico and its citizens are now paying the price,” the lawsuit reads.

The filing also takes a swipe at the southwestern Colorado town of Silverton, which sits just below the Gold King, for its reluctance to seek a Superfund listing to deal with the mine drainage. The town has reversed their trepidation and the EPA is in the process of designating its surrounding a federal cleanup priority.

The lawsuit against Colorado comes amid a flurry of legal action by New Mexico. In January, New Mexico filed the notices of its intent to sue with the EPA, Colorado and owners of the Gold King and Sunnyside mines, officials said.

In the state’s federal lawsuit filed in May against the EPA and the Gold King’s owner, it did not specify monetary damages, but state attorneys said New Mexico is entitled to at least $7 million to reimburse communities for emergency expenditures after the spill and for independent, third-party monitoring of water quality. In addition, the attorneys estimated New Mexico suffered economic harm of $140 million.

Lead levels in municipal water supplies continue to spike after storms, Flynn said in January after filing notices of intent to sue. That’s one of many long-term effects of the Aug. 5 blowout at the Gold King, which unleashed a torrent of mustard-yellow, acidic heavy-metals-laden runoff.

Flynn has accused EPA officials of shirking their duties for meaningful support and collaboration. And when New Mexico asked Colorado natural resources officials to provide information, invoking the Freedom of Information Act, the state received a bill for nearly $20,000 without the information, he said.

The EPA has said repeatedly it takes responsibility for the cleanup. Agency officials released data in late August that they said indicates surface water concentrations from the Animas River were returning to their normal conditions.

New Mexico and Colorado officials had been in talks for months, and Flynn said the state is still open to discussions in hopes of settling with the EPA and Colorado.

“We’re here out of necessity,” Flynn told The Associated Press on Thursday. “I would prefer to spend time and resources resolving this rather than duking it out in court.