By Luciano Costa
SAO PAULO (Reuters) - Four hydroelectric dams along Brazil's Rio Doce remain closed for an indefinite time after a deadly mining spill in November flooded the river with thick mud, according to water agency ANA.
ANA said in an emailed statement that only one of four hydro plants along the 800 km (497 mile) river, which runs through states of Minas Gerais and Espirito Santo, had requested to power up as the others continue to assess potential damage from the spill.
The bursting of a dam at the Samarco iron ore mine on Nov. 5 caused Brazil's worst environmental disaster, releasing between 30 million and 60 million cubic meters (7.9 billion to 15.9 billion gallons) of mining waste. The resulting flood killed at least 17 people, left hundreds homeless and polluted the river.
Samarco is a joint venture of Brazil's Vale SA and Australia's BHP Billiton.
The flood destroyed one tiny 1.8 megawatt hydrodam run by Grupo AVG and disabled others, which produce a combined 790 megawatts. The dams account for about 1 percent of Brazil's hydroelectric capacity, and their outage, though not a threat to the power supply, adds to an electricity crisis stoked by severe droughts and construction delays on the large Belo Monte dam.
Before ANA approves the restarts, further tests of the water quality need to be carried out as well as studies looking at the impact of power generation on other river uses. The river provides drinking water for several cities along its banks.
"The analysis has to be careful, so that the restarting of operations does not cause negative impacts on the river basin, which has already been significantly affected," ANA said in an emailed response to questions.
EDP Energias do Brasil, whose dam near the Atlantic Ocean is farthest from the accident site, said the accident did not affect its plant and has asked ANA for permission to restart.
Aliança Energia, a joint venture of Vale and Brazilian utility Companhia Energetica de Minas Gerais, or Cemig, said it was evaluating the impact of the disaster on its two plants on the river.
The Baguari hydrodam, owned by Neoenergia, Cemig and state-run utility Eletrobras' Furnas subsidiary, said it was checking its reservoir and water quality before asking to power up its turbines again.
(Writing by Stephen Eisenhammer; Editing by Lisa Von Ahn)