Brazil's Belo Monte hydroelectric dam in the heart of the Amazon will have fewer environmental effects than fossil-fuel alternatives and will be cheaper than other renewable energy sources, state media said Sunday.

Agencia Brasil cited a study by Federal University of Rio de Janeiro experts stating that alternatives to the controversial, $11 billion dam "would have bigger environmental impacts or would not have sufficient consistency to meet the anticipated growing demand for electricity in Brazil over the next few years."

"Belo Monte is an efficient project, which must be implemented. Brazil needs energy and any new energy generation has an environmental impact," Professors Nivalde Jose de Castro, Andre Luis da Silva Leite and Guilherme Dantas argued.

"In this study, it is clear that hydro-electricity offers a better cost-benefit in relation to other sources," Castro told Agencia Brasil.

The dam, which would produce more than 11,000 megawatts, or about 11 percent of Brazil's current installed capacity, would be the world's third biggest -- after China's Three Gorges dam and the Itaipu dam on the border of Brazil and Paraguay.

But its construction has been the subject of legal wrangling for decades.

The project also has come under international criticism, including from Oscar-winning movie director James Cameron of "Avatar" fame, who said rainforest indigenous tribes could turn to violence to block its construction.

But President Dilma Rousseff's government said the project should be allowed to go ahead.

The project is expected to employ 20,000 people directly in construction, flood an area of 500 square kilometers (200 square miles) along the Xingu river and displace 16,000 persons.

The government had pledged to minimize the environmental and social impact of the dam and asserted that no traditional indigenous land was to be affected.