Denver – Colorado Governor John Hickenlooper on Monday declared a “state of disaster emergency” over the accidental release of more than three million gallons (11.3 million litres) of potentially toxic wastewater from a defunct Colorado gold mine into local streams.

Hickenlooper said the order would free up about $500 000 from a state fund for response efforts to the spill, which was inadvertently triggered last week by a team of Environmental Protection Agency (EPA) workers.

The discharge, containing high concentrations of heavy metals such as arsenic, mercury and lead, was continuing to flow at the rate of 500 gallons (1 900 litres) per minute as of Sunday.

An unspecified number of residents living downstream of the spill who draw their drinking supplies from their private wells have reported water discolouration, but there has been no immediate evidence of harm to human health, livestock or wildlife, according to EPA officials.

Still, residents have been advised to avoid drinking or bathing in water drawn from wells in the vicinity, and the government was arranging to supply clean water to homes and businesses in need.

“We will work closely with the EPA to continue to measure water quality as it returns to normal, but also to work together to assess other mines throughout the state to make sure this doesn’t happen again,” Hickenlooper said in a written statement released by his office.

The Colorado Department of Public Health and environment was testing downstream water quality and wildlife officials are assessing the impacts on fish and other aquatic animals, the governor said.

The spill began on Wednesday after an EPA inspection team was called to the abandoned mine near the town of Silverton in southwestern Colorado to examine previously existing wastewater seepage.

By Friday, the main plume of the spill had travelled some 75 miles (120km) south to the New Mexico border, prompting utilities in the towns of Aztec and Farmington to shut off their intakes from the Animas River, one of the main waterways affected, local authorities said.

Agency officials said they were consulting with representatives of the Navajo Nation, whose sprawling reservation borders Farmington and the San Juan River.

In recent days, the EPA has been diverting the ongoing release into two newly built settling ponds where the waste was being treated with chemicals to lower its acidity and to filter out dissolved solids before being discharged to Cement Creek.

The creek’s water quality has already been badly degraded from a long history of acid mine drainage in the area, agency officials said.