The chief is especially exercised about the São Luiz do Tapajós (SLT) project, in which Siemens is not involved. It would dam one of the last big unobstructed tributaries of the Amazon (see map). The project would provide about a third of the hydropower that Brazil plans for the forthcoming decade, but it would also flood 376 square km (145 square miles) of land where the Munduruku hunt, fish and farm. “The Tapajós valley is our supermarket, our church, our office, our school, our home, our life,” explained Mr Kabá.

The Munduruku won a battle in August when IBAMA, Brazil’s environment agency, suspended licensing for the project, saying that Eletrobrás, the utility leading it, had provided too little information on its social and environmental impact.

That decision might still be reversed. Since it was made Brazil has impeached one president and installed another, Michel Temer. His priority is restoring growth to an economy suffering its worst-ever recession. The new government has put IBAMA’s decision-making, which many investors regard as too slow and cumbersome, under review.

The tussle over the Tapajós dam is part of a bigger fight about Brazil’s energy future. SLT is an example of a new sort of hydropower project, which floods a smaller area than traditional dams and therefore ought to cause less disruption and environmental damage. The massive Itaipu dam on the border with Paraguay inundated an area nearly four times as large. But critics of hydropower say “run of river” projects like SLT, which use a river’s natural flow to turn turbines, do not work as well as advertised. Though less destructive than conventional dams, which require bigger reservoirs, they still provoke opposition from people like the Munduruku. Other energy sources, such as gas and wind, are becoming more competitive. Brazil has “an opportunity” to rethink its energy policies, says Paulo Pedrosa, an energy official. 

Hydropower has long been Brazil’s main way of generating electricity. Most forecasts suggest it will remain so. The government intends to build more than 30 dams in the Amazon over the next three decades. The military dictators of the 1970s had little compunction about flooding vast areas of forest and displacing thousands of families. More recent (democratic) governments have turned to run-of-river dams. The world’s third-largest hydropower plant by output, Belo Monte on the Xingu river, opened earlier this year.

But newfangled dams have problems. More than conventional ones, their output of electricity fluctuates with the seasons. Belo Monte can produce 11,000MW when the Xingu is in spate, but less than a tenth of that in the driest months (September and October). Climate change may worsen the problem. Some climate models predict that river flows in large parts of the Amazon will fall by 30% in coming decades. Deforestation is delaying the onset of the rainy season in some areas by six days a decade, according to research published in Global Change Biology, a journal.

A river crawls through it

Drought can be expensive. In 2014 power from conventional dams dipped because of a dry spell, forcing electricity companies to buy from gas- and coal-powered generators at high spot prices. The risk of such fluctuations rises with run-of-river dams. Carlos Nobre, a former chief of research at the ministry of science, technology and innovation, thinks more frequent droughts will make future hydropower projects in the Amazon unprofitable.

Some energy planners think the answer to the shortcomings of run-of-river dams is to go back to the big-reservoir dams of the past. That is the solution favoured by Romeu Rufino, chief of Brazil’s electricity regulatory agency. It would eliminate the problem of variation in river flow (though not the risks that come with drought). The price would be causing environmental and social damage on the scale that earlier dams did.

New fuels may give Brazil other options. Its potential for solar and wind energy is among the highest in the world. The government has promoted them with lavish tax breaks. In the blustery north-east, wind power overtook hydropower this year; wind turbines now generate 36% of the region’s electricity, up from 22% in 2015. The Energy Research Company, a firm linked to the energy ministry, expects renewable generating capacity apart from hydropower to double by 2024.

Generators fuelled by natural gas have been hurt by the subsidies lavished on renewable energy. But, though less climate-friendly than hydropower, they are beginning to compete with it as a source of steady baseload electricity. Brazil now produces gas in abundance as a by-product of pumping oil from its offshore wells. Its marginal cost of production is nearly zero. The future of baseload energy is “hydro-thermal”, rather than hydro alone, says Adriano Pires of the Brazilian Infrastructure Centre, a think-tank in Rio de Janeiro.

What Brazil’s planners will ultimately decide is unclear. Decision-making is split among various agencies, including the energy ministry and the National Council for Energy Policy. Many officials, in their posts for decades, have pet projects, among them dams in the Amazon.

The recession gives them extra time to reconsider the future energy mix. It has caused a sharp and unexpected drop in electricity use; consumption is unlikely to return to its pre-recession level until 2018. By then, Mr Kabá and his allies hope, dams like the one that threatens to flood the Tapajós valley will be deemed obsolete.