Cachoeira dos Patos was never conceived alone. The Tapajos hydroelectric complex was a vision of the Brazilian electrical sector in the late 2000s and early 2010s - a cascade of six or seven hydroelectric stations on the Tapajos and Jamanxim rivers that together would add roughly 12,000 megawatts to Brazil's grid. The headliner was the Sao Luiz do Tapajos dam, rated at 6,133 megawatts, which would have been one of the largest hydroelectric projects anywhere. Jatoba was to provide 2,338 megawatts. Jamanxim, a dam on the same river as Cachoeira dos Patos, 881. Cachoeira do Cai added 802, Jardim do Ouro 227, and the disputed Chacorao 3,336. The appeal was clean baseload power from rivers flowing out of the Amazon basin. The problem was what each reservoir would flood.

The Cachoeira dos Patos reservoir would have flooded 9,000 hectares of Jamanxim National Park and 360 hectares of Jamanxim National Forest. Both are federally protected areas, one fully restrictive and the other permitting sustainable use. The reservoir would have spilled into the buffer zone of the Tapajos Environmental Protection Area and affected the proposed South Amazon Ecotones Ecological Corridor. These are not just lines on a conservation map. They represent the last continuous habitat corridors connecting the deeper Amazon to the southern savanna, and drowning them means losing the ability of species to migrate between biomes - a loss that biologists consider more consequential than the drowning itself.

The engineers designing the dam tried to solve the access problem with a genuinely novel approach. Most Amazon hydroelectric projects build roads - roads that persist, that become arteries for land-grabbing, illegal logging, and settlement that extends the damage far beyond the reservoir's edge. The platform approach rejected this. No access roads. Workers would be helicoptered in to temporary camps built on platforms above the forest floor. After construction ended, the camps would be dismantled and the site regenerated. Whether this would have worked, no one knows, because the project never proceeded. The concept had its critics - skeptics pointed out that the reservoir itself would be permanent, the turbines would be permanent, and the transmission lines from the dam to the grid would require maintained corridors through the forest for as long as the power flowed.

A December 2015 study changed the conversation about tropical hydroelectric projects in Brazil. Previous assumptions held that hydropower was essentially carbon-free. The study took into account methane and carbon dioxide emissions from reservoirs in the tropics - where decomposing vegetation at the bottom of warm, stratified reservoirs produces methane at rates that can rival fossil fuel plants. It concluded that the Cachoeira dos Patos reservoir, over its lifecycle, had a high probability of generating emissions comparable to a natural gas plant of similar output. The same problem that had already made the Balbina Dam into a notorious methane factory was likely to repeat here. A dam built to generate clean power might, because of what it drowned and what that drowning would slowly exhale, end up emitting nearly as much greenhouse gas as the fossil source it replaced.

The Federal Public Ministry, an independent branch of the Brazilian judiciary with authority to defend collective rights, issued its recommendation on July 29, 2013. The licensing process for Cachoeira dos Patos should be suspended, it said, for the same reasons as its sister dams on the Tapajos, Teles Pires, Jamanxim, and Juruena rivers. The legally required Integrated Environmental Assessment had not been done. The Munduruku and other indigenous peoples whose territories would be affected had not been consulted - a consultation required under both Brazilian law and the Indigenous and Tribal Peoples Convention, which Brazil signed. Two months later, on September 20, the Ministry of the Environment complied. Licensing was suspended. Aneel's feasibility study deadlines, already pushed from 2011 to 2013, were allowed to lapse. The dam was not built. The river still runs. The Jamanxim, for now, flows freely from its sources to the Tapajos, carrying what it always has.