The Munduruku have lived along the Tapajos and its tributaries for centuries, building their identity around the river's rhythms and the forest that lines its banks. In 1990, an estimated 529 people inhabited the Sai Cinza territory. By 2000 the population had nearly doubled to 1,022, and by 2013 it had reached 1,739. This growth reflects not just births but a community consolidating itself, organizing through institutions like Associacao Da'uk, the Conselho Indigena Munduruku do Alto Tapajos, and the Kerepo producers' association. The Associacao Indigena Wuyxaxima adds another layer of governance. The territory sits in the municipality of Jacareacanga, bounded by the Tapajos to the west and north, with the Mundurucu Indigenous Territory pressing against its southern edge. In the eastern portion, the territory straddles both sides of the river. The forest cover tells its own story: 82.69% dense rainforest, the rest a transitional zone where savanna meets jungle, a biome contact area that produces ecological conditions found nowhere else in quite the same combination.

Brazil's appetite for hydroelectric power has reshaped entire river systems across the Amazon. The Tapajos basin was no exception. Plans for the Chacorao Dam envisioned a reservoir that would have swallowed portions of two indigenous territories, displacing Munduruku, Kayabi, and Apiaca communities. But the constitution's prohibition on forced relocation of indigenous peoples created an insurmountable legal barrier. As of 2010, Eletronorte had not even applied to begin feasibility studies, because without a regulatory decree permitting construction in indigenous territories, there was simply no legal pathway forward. A spokesman acknowledged the impasse plainly: the law left no room. The Munduruku's resistance to dam projects across the Tapajos basin has since become one of the most prominent indigenous environmental campaigns in Brazil.

Rather than waiting for outsiders to decide the territory's future, the Munduruku began shaping it themselves. In November 2011, a series of planning workshops brought together more than 300 indigenous participants from both the Sai Cinza and Mundurucu territories. By October 2013, a formal seminar was held in the village of Sai-Cinza to develop a Territorial and Environmental Management Plan, known by its Portuguese acronym PGTA. Representatives from every part of both territories attended, alongside government officials and civil society organizations. The PGTA process represented something larger than land management: it was an assertion of sovereignty, a declaration that the people who knew these forests best should be the ones deciding how to steward them.

Legal recognition has not made Sai Cinza impervious to outside pressure. Thirteen mining concessions operate in the surrounding region, and the territory's proximity to the gold-rich Tapajos corridor means the threat of illegal incursion is constant. The Fundacao Nacional do Indio, Brazil's indigenous affairs agency, maintains a presence in the territory, but enforcement across 126,000 hectares of remote jungle is an enormous challenge. Evangelical missions from the Assembly of God and the Brazilian Baptist Convention have also established themselves within the territory, adding cultural complexity to an already layered situation. The Sai Cinza territory was formally declared by decree on 14 July 1987 and approved on 26 December 1991, but its real protection comes less from paperwork than from the Munduruku themselves, who have proven willing to organize, resist, and plan for a future they intend to define on their own terms.