Republican senators marked the one-year anniversary of the Gold King Mine disaster in Colorado by praising the beginning of a criminal investigation into the incident.

The mine disaster was caused when Environmental Protection Agency contractors attempted to unplug an abandoned gold mine in Silverton, Colo., on Aug. 5, 2015, causing a 3-million gallon blowout of toxic wastewater that sullied the waterways of three states.

"The EPA has done a poor job of taking responsibility for the spill, cleaning up the toxins, helping the farmers and families affected, and remaining transparent throughout this process," said Sens. John Barrasso, R-Wyo., and John McCain, R-Ariz, in a joint statement.

The two lawmakers led the charge in the Senate to hold the EPA accountable for the spill that has plagued tribal communities along the San Juan and Animas river system that the toxic plume had affected the most.

The spill affected the waterways of Colorado, New Mexico and Utah. EPA said the spill was equal to four days of the normal wastewater runoff from abandoned metal mines.

"Farmers and ranchers on the Navajo Nation have lost a year's worth of income to provide for their families and still don't know the long-term effects of the spill," the senators said. Barrasso is chairman of the Indian Affairs Committee.

"We are glad that a criminal investigation is taking place, as this is an important step in providing accountability for the EPA's negligence," the senators said. "We must make sure that this kind of catastrophe is never repeated."

The EPA inspector general announced in the last week that a criminal probe had been initiated with the Justice Department to assess criminal intent in the aftermath of the spill.

McCain and Barrasso had sent a letter in May asking Attorney General Loretta Lynch to initiate a criminal investigation into the spill.

The GOP in both the House and Senate have called for a senior EPA official to be held accountable for the spill.