He made the pledge before hundreds of activists that protested Monday in Brasilia against the proposed Belo Monte Dam, which will displace some 50,000 Indians and small farmers.
Cameron added his voice to the protest at an event held in front of the National Electric Energy Agency, which is soliciting bids on the massive project.
The filmmaker said that during his two weeks in Brazil, where he took part in meetings of environmentalists and has distributed the DVD of “Avatar,” he heard “dozens of people” speaking out against the project because of the consequences it will have for the environment and for natives of the Amazon.
Together with Cameron were “Avatar” stars Sigourney Weaver and Joel David Moore.
The Belo Monte project would involve diverting a 100-kilometer stretch of the Xingu River, an Amazon tributary, and directly affect 12,000 families, including residents of two indigenous hamlets whose survival would depend on the dam operator providing them excess water from the reservoir.
Sixty-six municipalities in the Amazonian state of Pará will be totally or partially inundated if the complex is built.
The proposed US$ 10.6 billion hydroelectric dam would be the world’s third largest after China’s Three Gorges Dam and Itaipu, which is shared by Brazil and Paraguay.
The Brazilian Attorney General’s Office said last week that it plans to seek the revocation of the environmental license for Belo Monte, citing the “serious impact” it could have on the Amazon jungle.
Brazil’s government insists the dam is needed to meet the burgeoning energy needs of Latin America’s biggest economy.