Vietnamese authorities say they are carrying out inspections at a controversial bauxite-mining plant where a break in a waste containment reservoir caused a spillage of sludge last week, raising public alarm about its environmental impact, according to reports.

Local news organizations that reported on the spill at the Tan Rai bauxite plant in Lam Dong province in southern Vietnam’s central highlands cited scientists who had previously warned about the adverse environmental effects of such reservoirs if they overflow and pollute rivers.

According to reports, red-colored sludge flowed out of the reservoir at the plant after the embankment gave way.

But the Vietnam National Coal and Mineral Industries Group (Vinacomin), which owns the plant, and the Ministry of Natural Resources and Environment said the sludge was not what is known as red mud, a toxic byproduct of the process that refines bauxite, raw aluminum ore, into aluminum oxide, or alumina.

Because the majority of Vietnam’s bauxite reserves are located at high elevations in the central highlands, any breaks in waste reservoirs pose the threat of flooding low-lying areas.

A red mud reservoir is believed to be located four kilometers (2.5 miles) from the burst reservoir at Tan Rai, located in Loc Thang town in Lam Dong province’s Bao Lam district about 700-800 meters (2,300-2,624 feet) above sea level.

“If a [red mud] reservoir breaks [in an area of high elevation], all the areas below will be flooded as with flash floods, jeopardizing the ecology, damaging people’s gardens and [potentially] killing animals and people who are exposed to the red mud,” Le Huy Ba, director of the Institute for Environmental Science, Technology and Management at the Ho Chi Minh University of Industry in Ho Chi Minh City, told RFA’s Khmer Service.

The Tan Rai reservoir, which has a total capacity of 2 million cubic (70.6 million cubic feet), holds waste and water discharged from the ore-cleaning process, a report by state-owned Vietnam News said.

It discharged about 5,000 cubic meters (176,573 cubic feet) of sludge on Oct. 8 when an embankment broke and spilled its contents into Cai Bang Lake, said the report, citing Lam Dong Province’s Department of Natural Resources and Environment as the source.

Authorities contend that the spillage has not harmed local residents or crops.