But with hurdles ahead, including opposition from President Rafael Correa, it's far from clear what will happen to the ITT oil block that the administration says holds 20 percent of the nation's crude reserves.

Last week, Correa announced that the country was cancelling a six-year-old plan that aimed to keep more than 840 million barrels of oil untapped in perpetuity beneath the ITT if the international community would contribute $3.6 billion. The money never materialized and Correa said he had no choice but to tap the oil, which lies in a remote part of the 2.4-million acre Yasuní National Park.

The Yasuní-ITT Initiative, as it is known, is popular in Ecuador, where more than 80 percent of the population backs the plan. And that has led to a grassroots effort to save the forest.

On Thursday, a coalition of environmental and indigenous groups took the first step in that fight by taking a proposed referendum question to the Constitutional Court. The question reads: Are you in agreement that the Ecuadorean government keep the crude in the ITT, known as block 43, underground indefinitely?

The court has to rule if the question is constitutional. But that's only half the battle. In order to get the question before the public, the groups would need congressional support or to collect more than 584,000 signatures — 5 percent of all registered voters — to trigger the plebiscite.

Correa says the country needs the oil resources to fight poverty and he's bristled at the idea of a referendum. He's accused independent media, which he has a long-running battle with, of playing politics with the issue.

"Now the biggest environmentalists are the mercantilist newspapers," he wrote on Twitter. "If we have a national referendum we'll also propose that newspapers be digital-only to save paper and avoid indiscriminate logging. We'll see who's who. Don't let yourselves be fooled."

Correa has said that the state-run oil company will use cutting edge techniques to minimize the impact of oil exploration and that less than one tenth of one percent of Yasuní National Park will be affected. Conservationists worry about any industrial activity in the area that is one of the most biodiverse spots on the planet, brimming with unknown species.

The decision to pull the plug on the process means the government will have to return a portion of the funds received. Authorities have said the Yasuní-ITT initiative generated some $337 million in donations — but much of that was technical support and other non-cash cooperation.

The United Nations trust fund that was set up in 2010 to receive donations has $10.2 million in the account. Under the rules of the fund, only those who made donations larger than $50,000 — and requested a certificate of guarantee — will get their money back. On Friday, the U.N. said it was up to the Ecuadoran government to provide information about the amount of funds under guarantee.

Ecuadorean officials are expected to meet in coming days to decide how to unwind the trust fund.

On Thursday, Ivonne Baki — the government's chief fundraiser for the project — defended her work. Speaking at a farewell event, she said that with a budget of $7.3 million over three years, her team of 15 people managed to make the initiative the most "emblematic" project of Correa's administration.

She also said she would keep defending the park and called on the president to create a biodiversity study center to share the forests' knowledge "with the world."

"The Yasuní-ITT Initiative would have set a precedent for the world to follow that would have changed the history of humanity," she said at the event. "But there were many people who resisted that possibility."