Officials in towns downstream from where millions of gallons of mine waste spilled into a southwest Colorado river are demanding answers about possible long-term threats to their water supply.

Colorado and New Mexico declared stretches of the Animas and San Juan rivers to be disaster areas as the orange-colored stream of waste made its way downstream toward Lake Powell in Utah, after spilling on Wednesday at the abandoned Gold King mine near Silverton, Colorado.

Workers with the US Environmental Protection Agency accidentally unleashed the spill as they inspected the abandoned mine site. The 11 million liters of waste included high concentrations of arsenic, lead and mercury.