ALBUQUERQUE, N.M. » New Mexico officials said today they plan to sue the federal government and the owners of two Colorado mines that were the source of a massive spill last year that contaminated rivers in three Western states.

The New Mexico Environment Department said it filed a notice of its intention to sue the U.S. Environmental Protection Agency over last year’s spill. The lawsuit would be a first and also would target the state of Colorado and the owners of the Gold King and Sunnyside Mines.

An EPA cleanup crew accidentally unleashed millions of gallons of contaminated wastewater in August at the inactive Gold King mine near Silverton, Colorado. It fouled rivers in Colorado, Utah and New Mexico with contaminants including arsenic and lead, temporarily shutting down drinking-water supplies and raising concerns about long-term effects to agriculture.

The New Mexico regulators said they will sue if the EPA does not begin to take meaningful measures to clean up the affected areas and agree to a long-term plan that will research and monitor the effects of the spill.

“From the very beginning, the EPA failed to hold itself accountable in the same way that it would a private business,” said Ryan Flynn, state Environment Department cabinet secretary.

A spokeswoman for the EPA did not immediately return an email from The Associated Press.

The lawsuit is believed to be the first formal intention to sue the EPA over the spill. It occurred when workers for the agency and its contractor, Environmental Restoration LLC, started excavation work that was intended to allow them to safely drain the mine.

The accident prompted harsh criticism of the EPA for failing to take adequate precautions despite warnings that a blowout could occur.

But Interior Secretary Sally Jewell said a review by her agency showed the spill was “clearly unintentional.”