After years of construction, the Tocantins river was eventually blocked with the inauguration of the dam in 1984 and is since then run by Eletronorte, a subsidiary with mixed-ownership, controlled by Brazil’s federal utility holding company Eletrobras. 

A case study on the social impacts of the Tucuruí dam by Fearnside (1999) reported a systematic overestimation of the plant's benefits by public authorities, while social and environmental impacts have rather been downplayed, making it an example of Brazil’s unlearned lessons in hydroelectric development. It notes that most generated power was used for the highly subsidized aluminum industry in Barcarena and São Luís. 

The number of displaced people has been much higher than initially communicated and the created local employment remained minimal. Significant parts of the displaced population were not included in Electronorte's estimates of the affected communities and therefore excluded from the official resettlement program; the company arbitrarily provided some small cash payments but relieved itself from any further responsibility (such as providing land), triggering disruption and indignation among the displaced traditional population who formerly largely lived from small-scale extraction of resources and subsistence agriculture. 

The dam introduced the plague of Mansonia mosquitos that exacerbated incidences of malaria diseases, inundated riverside forests, affected the local fauna and aquatic environment, leading to an increase in mercury concentration and the collapse of fishery and shrimp numbers soon after, and with that a decline in fishing and local food supply. While the dam brought an overall increase in population, it affected in particular indigenous populations as three reserves were partly flooded and four others cut by transmission lines. The rerouting of the Transamazon Highway and establishment of resettlement areas caused further expropriation of indigenous livelihoods as well as heavy deforestation.  

In 1991, the Brazilian government was condemned for the impacts of Tucuruí by the International Water Tribunal held in Amsterdam. Although this did not trigger legal consequences, it brought international attention to the conflict. [8] A 2001 follow-up study stated that access to information by the public had been restricted by Eletronorte while decision-making in the course of the project virtually ignored environmental studies and was importantly influenced construction companies, the military, and foreign financial interests, ultimately serving the interests of multinational aluminum companies. [9] 

Beyond the displaced people, also nearby municipalities and agricultural producers suffered from indirect impacts, for example, increased dryness from the cease of seasonal floods or the proliferation of socioeconomic health impacts (e.g. alcoholism, depression, stress) related to the change in livelihood and culture. The consequences also led to an intensification of land occupation in the Tucuruí area – typically by displaced families trying to build up a new existence – and with that increased conflict with Eletronorte and other large landholders. The occupations – who received support from Brazil’s landless mass movement MST (Movimento dos Trabalhadores Rurais Sem Terra) - also included public land that was irregularly grabbed and deforested by large-scale ranchers and about 1500 islands in the artificial Tucuruí lake. 

More than 25 years after being displaced, most of these communities are still waiting for compensation and lack basic public services [10] [11]. As it was reported in 2013, 12,000 people in the immediate surroundings of the hydroelectricity plant, including the landless people on the lake islands, lived without electricity, despite numerous political promises in the past. 23 % of the population of Tucuruí city lived in favelas [12a]. 

A study by Arrifano et al. (2018) found alarming levels of mercury concentration and resumed that “inhabitants of the Tucuruí Dam seem to show the highest levels of total mercury ever detected in human populations living near an Amazonian dam” [12b].

The hydroelectric dam and related megaprojects have thus aggravated conflicts over land and resources, triggered socio-environmental transformations, and in doing so, also brought forward the emergence of new social actors, as for example Silva (2009 and 2014) outlines. Local movements such as the Comissão dos Atingidos pela Hidrelétrica de Tucuruí (CAHTU) and the ‘Movement of the expropriated people by the Tucuruí dam’ (Movimento dos Expropriados pela Barragem de Tucuruí) emerged in the early 1980s, building one of the historical roots of Brazil’s 1991 founded Movement of People Affected by Dams (MAB, Movimento dos Atingidos por Barragens) which over the last three decades has led social mobilizations against displacements and related human rights violations related to hydroelectric as well as mining dams. Supported by rural worker unions and the Comissão Pastoral da Terra (CPT), the social mobilizations in Tucuruí gave voice and new identity to marginalized local groups who would now express claims against Eletronorte and public authorities and publicly uncover socio-territorial and environmental conflicts. [6][7][13] 

Since the beginning of the dam’s construction, affected communities of the lower Tocantins river had issued complaints against the dam. Protests included frequent demonstrations, occupations of public administrations and a two-years lasting camp at the entrance of the Eletronorte compound to demand alternative settlements and compensation for their destroyed economies and livelihoods. [8] [10] Moreover, as it is documented by the Fiocruz Foundation, an association of island communities together with the local movements had been demanding the creation of the ‘Itaipava Extractivist Reserve’ (RESEX) on the Tucuruí lake since the early 1990s, with the objective to protect both the environment and allow local families to self-manage their livelihoods – Extractivist reserves also became in Brazil a strategy against regular violence by land owners, concession holders and loggers. 

This proposal was discouraged by the government's proposal for the creation of a ‘sustainable development reserve’ (Reserva de Desenvolvimento Sustentável; RDS) – the major difference being that the latter would ensure greater flexibility when it comes to future economic activities and constructions in the area than the status of a RESEX. [10]. It was finally left aside with the announcement of the expansion plans of the Tucuruí dam and the second construction phase.

Mass mobilizations also continued in the 2000s. For example, street demonstrations led by the MST, the MAB and Via Campesina resulted in a two-days occupation of the Tucuruí plant in 2007, forcing government representatives to hold talks with the MAB. Other protests were directed against public authorities like INCRA (National Institute for Agrarian Reform; responsible for agrarian reform and resettlement) in order to regularize the occupied islands and settlements of around 5.000 displaced families; for example, about 220 landless peasants occupied the seat of INCRA in Tucuruí in 2009. Such protests however led to an increasing criminalization and detention of leading activist in the region, including MAB leaders of the Tucuruí occupations (one of them for example condemned to 12 years in prison), but also the solidarity of other social movements [11][14][15][16][17]. 

Another notable example is the 2007 occupation of the Piratininga ranch by displaced and landless communities and the MST movement, establishing a settlement named Salvador Allende. The MST considered the area as public land that was appropriated through the common practice of grilagem (a form of large-scale land-grabbing using falsified documents, often involves violence). After various violent incidents, including conflicts with loggers and various armed attacks, a part of the initially involved 480 landless families left the territory. In the following year, about 1300 families of different locations occupied INCRA headquarter in Macabá. Also the MAB as well as the Federação dos Trabalhadores e Trabalhadoras na Agricultura Familiar (Fetraf) started to support the occupation and also denounced the deforestation of protected areas, violence by loggers and a lack of support by public authorities. In 2012 – after the putative land owner Renato Lima could not prove land titles – the Salvador Allende settlement was officially regularized by INCRA and distributed in small agricultural lots to a number of families [2][11]. 

In 2013, the Federal Court of Justice granted state compensations to the Asurini indigenous community. At the same time, new protests took place, most notably hundreds of people occupied the city council of Tucuruí in order to once again demand the regularization of land and the realization of sustainable development plans for affected communities that were agreed in 2005 with public authorities and Eletronorte but had not been implemented [10][18]. Also in the most recent years, and 30 years after the first displacements, the MAB and aligned movements have continued to mobilize and to demand compensations and public support for affected people; annual mass demonstrations take place around the 14th of March on occasion of the international day of rivers and the struggle against dams [10][19].

The movement has been regularly confronted with acts of violence. In 2009, the trade unionist Raimundo Nonato do Carmo Silva, know as Raimundinho, was assassinated in Tucuruí. As a head of the Sindicato dos Trabalhadores Rurais (STR), he had dedicated his life to the support of expropriated families and had been an advocate for land reforms and the establishment of protected areas and extractivist reserves in the Tucuruí area [16][20]. On March 22, 2019, the regional MAB coordinator Dilma Ferreira da Silva, her partner Claudionor Costa da Silva, and friend Hilton Lopes were found brutally assassinated at Dilma’s house in the settlement of Salvador Allende, located close to kilometer 50 of the BR-422 road in the province of Baião. According to first reports of neighbors, five people arrived at the house in the night before and then music was played unusually loud and long. When on the next day the school bus stopped by the house to pick up Dilma (who worked in the local school), the murder was discovered without clear indications of the circumstances. The police spoke of an “execution” and signs of torture. Also, the United Nations High Commissioner for Human Rights and deputies in the Brazilian Congress condemned the killing, while the Bolsonaro administration did not issue a statement of any kind [2] [3] [21] [22] [23]. 

Two days after, another three people were found assassinated in a nearby farm, owned by a large-scale rancher and businessman Fernando Ferreira Rosa Filho. The victims were assumed to be irregularly employed workers of the farm. According to the first police investigations, the crimes were related and committed by the same group. Shortly after, the police released the names of four alleged executors – who, by April 2019, are still fugitive - and arrested Fernando Filho who was suspected to have ordered the assassinations. While the exact motives were unknown up to that point, a first police hypothesis assumed that Fernando Filho, the landowner of the site where the second killing took place, was about to build a clandestine airstrip for illegal drug trafficking and assumingly wanted to get rid of interfering employees and neighbors linked to social movements. He had also been suspected of other crimes in the region before. [4][24][25][26] However, these tragic incidents can also be understood in a wider context of agrarian conflict and its exacerbation through mega projects that have caused displacement and the violation of basic rights.

As the CPT noted in a statement, Dilma Silva was the first assassinated land rights activist in the Amazon in 2019. As the regional coordinator of the MAB since 2005, she was working with local groups of affected people and, as outlined above, was living on land that had been under dispute. [2] The MAB pointed to the international recognition of Dilma’s activism and her lifelong struggle against multiple discriminations – as a black, female, northeastern, riverine and migrated person affected by one of the most conflictive and emblematic giant dam projects in the Amazon. Dilma Silva was displaced with her family during the second construction phase of the Tucuruí dam in the 2000s and had lived in the Salvador Allende settlement for five years after becoming displaced. With the MAB she had made public statements against a systematic pattern of human rights violations in the construction of dams across Brazil, proposed policies for the rights of those affected by dams and called for special attention to impacts on women. The claims included government compensation for lost property and livelihoods and public services in new settlements. 

However, little to nothing of that has been implemented up to that point. Displaced people in many settlements still lack electricity, basic sanitation, piped water as well as transport and health services, and a program for monthly basic food provision was cut by Brazil’s former government. [3][22] While crimes against environmental activists often go unpunished, and the killings form part of a series of recent violent incidents against the landless movement, public authorities have reacted unusually fast in this case. In an interview with Mongabay, MAB’s national coordinator Iury Paulino noted that the “rapid response of the State, in this case, is proof that if they want, they are able to mobilize resources and find answers. Unfortunately, the discovery of the culprit alone does not solve the problem of those affected by the Tucuruí [hydroelectric] plant. Crimes will continue to happen as long as there are much misery and inequality in the region due to the State’s omissions.” [3] A public statement signed by 99 environmental and human rights organizations and the MAB shortly after noted that the “assassination of Dilma Ferreira Silva is evidence of the grave situation faced by human rights and environmental defenders in Brazil, a country that tops the global ranking in violence practiced against defenders, with one person murdered every six days in 2017” [27] and blamed Brazil’s new government under president Bolsonaro for the recent intensification of the undermining of environmental legislation and human rights, especially affecting indigenous groups, quilombolas and family farmers. [27]

Installed Capacity: 8,370 MW

Annual Production: 41.43 TW-hour

Area Flooded: 3,014 km^2 = 301400 hectares

Cost: USD $5.5 billion [1]