James Cameron and Sigourney Weaver are the latest to wade into the battle to stop the Belo Monte Dam in Brazil but it seems celebrity causes are less likely to win ecological battles than they were 20 years ago and with oil and gas prices spiralling big dams are back on the menu everywhere.

In the 1990s Sting and the Xingu tribal people succeeded in creating enough worldwide protest to stop the Belo Monte dam being put into construction. Since then the World Bank has stepped away from financing big dams, distancing itself from projects which have often caused as many problems as they solve.

One fifth of the world's freshwater is found in the Amazon. The Belo Monte dam will divert a significant amount of the Xingu river flooding 640km including much of the city of Altamira and displacing upwards of 20,000 people. It will cost $17 billion and environmentalists argue that this is only viable because it will lead the way for dams further upstream which could produce far more energy and because the electricity will power aluminium smelters and iron ore mines. They also site the devastating impact on wildlife and migratory fish which are staples for indigenous tribes, a likely increase in malaria from the stagnant water and significant methane release from the river bed as it dries.

The Brazilian government, and many Brazilian people, argue that the dam is absolutely necessary and that this is renewable energy. With one of the world's fastest growing economies they need fuel, and hydro already provides 80% of the country's energy needs. Should privileged Western stars be listened to when they may not fully understand the issues and what is more important to the environment movement, conservation or carbon?