An estimated 200 indigenous people from Brazil's Amazon region have occupied a work area at the Belo Monte dam construction site, at least partially halting work on the controversial mega project on the Xingu river.
The indigenous people are from at least four tribes - the Xikrin, Juruna, Parakana and Araras - and are protesting against what they say is the negative effects of the construction.
They say the construction runoff is muddying the waters and drying up parts of the river they use to fish.
They are also upset that mitigation projects or compensation promised to the indigenous people by the builders to minimize effects of the construction have been slow to materialize.
The indigenous people have occupied one of work sites of the dam since last Thursday, making it the longest occupation of its kind on the construction site.
Click here to watch a video, shot by the Indian tribes during the opening phase of their occupation of a work site:
The builders have halted work on the part of the dam that is being occupied by the indigenous people, but say work continues unabated in other areas. (The construction site is so big it's divided up into multiple work sites).
According to a local federal prosecutor, the builders' judicial request to have the Indians removed by force by police was rejected by a federal judge over the weekend.
The Belo Monte Dam is the most controversial construction project in Brazil. It is scheduled to cost roughly $14bn, and the first turbine is expected to be operational by February 2015.
Click here for an Al Jazeera multimedia presentation on the Belo Monte Dam
When completed, the dam will be the third largest in the world.
The Brazilian government says Belo Monte will provide much needed energy at minimal environmental impact. They also argue that hydroelectric dams are clean energy.
But environmentalists have said for years the social impacts - displacement of thousands of people, mostly indigenous people - not to mention environmental damage, are far worse than any potential benefits.
The dam, which was first proposed in the 1970s, has gone through numerous judicial and environmental injunctions in the past couple years. But with most of the hurdles seemingly passed last year, construction on the dam began in July 2011.
The construction ramped up in January this year.
As for the protest by Indians, nobody knows where this will go from here.
On Thursday a delegation from the capital Brasilia will arrive at the work site to speak directly to the Indians to try to reach a compromise.
In the meantime, hundreds of more indigenous peoples are reportedly in boats making their way to provide support.
In late January, I visited the construction site, and towards the end of the day the builders said we had to move away from the immediate work area. Why, I asked? Because there will be an explosion, we were told. A couple of times a day engineers use dynamite to blast away hard rock to make way for the dozens of bulldozers.
I saw the explosion. It's powerful symbolism that could easily be interpreted as the builders' way of saying: The time for debate is over, this project is moving forward.
As we are witnessing now, the indigenous people didn't get the memo.
With the occupation of the dam work site they too are sending a clear signal:
The final chapter in the fight against this mega dam in the Amazon has yet to be written.