Plans by the Spanish- and Italian-owned Endesa energy company to carry out a hydroelectric project on Chile’s Puelo River are attracting opposition on both sides of the Chilean-Argentine border.

Located in northernmost Chilean Patagonia, the Puelo River, Chile’s second largest river in terms of volume, flows from Argentina’s Lake Puelo. Two-thirds of its estimated 2.17-million-acre (880,000-ha) watershed occupies the Argentine side of the Andes.

The Puelo watershed spans two new United Nations Biosphere Reserves, both of which were officially announced in September by the United Nations Educational, Science and Culture Organization (Unesco).

These Chilean and Argentine temperate-rainforest reserves are eventually to be merged to form a binational Southern Andes Temperate Rainforest Biosphere Reserve.

The importance of the Puelo, both to the UN and to Argentina, could make this emerging eco-conflict at least as controversial as the contentious debate in Chile over plans by Endesa and its Chilean partner, Colbún, to build four dams on the Baker and Pascua rivers in the southern Patagonian region of Aysén.

“This isn’t just a Chilean problem,” says Alejandro Yanello of Ecopiuke, a green group in Argentina. “Any modification of the watershed affects ecosystems in both countries.”

Cross-border cooperation

Says Mauricio Fierro, founder and president of GeoAustral, a Puerto Montt-based environmental group that is leading opposition efforts in Chile: “This is a real disaster. We are working closely with our Argentine friends to definitively halt this project.”

Fierro, who has been tracking the project since the idea for the dam first surfaced many years ago, says citizen opposition will be fierce when Endesa workers begin to carry out work for the environmental-impact study later this year. “We will not let them on the land,” he says. “We will block them however possible from entering the areas they intend to destroy.”

Last November, the company announced long-held plans for the Puelo dam, called El Portón. The proposed 320-megawatt dam is to be accompanied by two run-of-the-river dams, called El Steffen, slated for the nearby Manso River. Combined the three dams would have a capacity of 685 megawatts. The company puts their cost at US$822 million and forecasts the project will be complete sometime after 2016.

Given Chile’s faltering supply of natural gas from Argentina and the swelling cost of diesel fuel for power generation, business and government interest in new hydropower is keen. Endesa has stoked that interest by forecasting its Puelo project could yield the equivalent of 10% of Chile’s current power supply.

Plans for El Portón and El Steffen mark a significant scaling down of an earlier blueprint for a dam that would have been built farther upstream on the Puelo near Lake Tagua and would have ranked as Chile’s largest dam.

An Endesa spokesperson declined to comment for this article. But in a report issued last year, Endesa asserted that under the revised version, up to 80% less land would be flooded, meaning the waters would not inundate prized stands of southern Chile’s massive alerce trees (Fitzroya cupressoides). And destruction of Lake Tagua and several other lakes in the area would be avoided, the company says.

Green advocates and residents worry the impacts still could be extensive. They point out that El Portón would flood 12,000 acres (5,000 has) that include large stretches of native forest as well as habitat of the endangered huemul deer (Hippocamelus bisulcus).

Downstream impacts alleged

Critics also assert that by blocking river flow, the project would significantly decrease oxygen content in the Reloncaví estuary, a large Pacific-coast bay. That, they add, could harm marine species throughout the bay, including farmed salmon and shellfish in dozens of the area’s aquaculture operations.

“If the oxygen is cut off, the salmon farms in Reloncaví would disappear and fishing would be near impossible,” says Rodrigo Condeza, director of a local trekking and outdoor-adventure company in the area.

Adds Condeza, a co-leader of the Citizen’s Committee for the Defense of Puelo: “The Puelo watershed is an important part of the local tourism economy. There are fly-fishing lodges all over the area. [And] farmers who have lived here for decades will be forced to leave.”

GeoAustral’s Fierro, meanwhile, points out that El Portón is slated for a region of seismic and volcanic activity. After the eruption last month of Chile’s Chaiten volcano, tremors of up to 5.3 on the Richter scale shook the area, according to the U.S. Geological Survey.

Across the border, Argentines are supporting Chilean activists not only out of solidarity, but because they worry that damming of the Puelo could contaminate water, disrupt water levels and alter the micro-climate in El Bolsón and other Argentine towns in the watershed.

Argentine authorities have yet to make pronouncements on the project, but some local officials have publicly expressed concern.