Brazil's new president, Dilma Rousseff, has never been popular among environmentalists.

Since the early days of predecessor Luis Inácio Lula da Silva's presidency, when she occupied the post of minister of mining and energy, many activists have seen her as a leader with an old-fashioned view of development. Something like "economic growth is priority number one, no matter if some hectares of Amazon rainforest has to be chopped down".

The animosity increased even more after Rousseff was promoted, in 2005, to the ministry of internal affairs – the post that paved her way to the presidency. With the second most important job in the republic, she was responsible for coordinating the government action plan, the Plano de Aceleração do Crescimento (PAC) – the "plan of growth acceleration".

It was a period when almost every infrastructure project – from offshore oil drilling to roads in the middle of the forest – were given licences, despite civil society criticism.

Nevertheless, in her first day in the job, the new president gave an impression that something could have changed. After being sworn as the 40th Brazilian president and the first woman to assume the post in the country, Rousseff told the crowd: "Brazil has the holy mission to prove to the world that it is possible to have speedy growth without destroying the environment." The speech was interpreted as a sign that the new administration would act on issues such as clean energy and deforestation.

But less than a month on from the inaugural speech, non-governmental organisations are saying they were no more than empty words: the new administration soon sacked the president of the country's environmental agency (Ibama) and then authorised the construction of the controversial Belo Monte hydroelectric power plant.

First conceived by the military government in the 1980s, the dam will be located in the heart of the Xingu river, a place known for its unique coverage of rainforest and numerous indigenous tribes.

The licence obtained last week by Norte Energia SA – a consortium almost entirely funded by state money – allows 238 hectares of forest to be cut down in order to open roads and basic infrastructure for the workers. And this is just the beginning; when it starts operating, Belo Monte's reservoir is expected to flood almost 60,000 hectares of land.

The problem is that Norte Energia has not yet figured out how to avoid all the indirect environmental impacts that the promise of jobs and wealth will bring to the region. Some estimates claim 10,000 people are already moving into the Xingu area and up to 100,000 are expected to arrive in the next few years.

Felício Pontes, a public attorney from the state of Pará, said the new licence could not, by law, be issued without a solution being found for the problems it will cause. In other words, green light for construction cannot legally happen without more hospitals, sanitation and security in the region. Pontes and his team have already petitioned the federal court asking for the suspension of the licence.

But even if the law stops the project, Belo Monte seems to be a point of no return for Rousseff: the dam is supposed to be one of the biggest achievements of her government and it is considered, after all, clean energy.

Back in 2004, when she was Lula's minister of mining and energy, Rousseff represented Brazil at the World Renewable Energy Conference, called by the German government. During negotiations, she announced that Brazil would block the consensus if big hydroelectric dams were not considered a form of clean energy. The Germans, who had previously only wanted to put small-scale dams in the renewable category, ended up accepting the Brazilian demand.

At that time, I had the opportunity of interviewing the future president and I asked her why she was taking that combative posture. "We have to be watchful, because it seems to me that some countries are trying to push technology to the developing countries," she said. Not surprisingly, in 2009, when Rousseff was the head of Brazil's delegation to the Copenhagen climate summit, she adopted a similar narrative, claiming the north was depriving the south of its right to develop.

However, like Lula, Rousseff's performance on environmental issues will be mainly assessed by the Amazon deforestation rates. Controlling deforestation means curbing the main source of greenhouse gas emissions in Brazil and, to the public, it is also a demonstration of a strong hand over the land tenure chaos that still reigns in the forest.

By toughening the police and drying financial credit for illegal loggers, Lula managed considerable advances, cutting two thirds of deforestation in less than six years. The positive trend even allowed his government to offer an ambitious target within the UN climate change convention: an 80% reduction of Amazon deforestation by 2020 compared with the average of the five previous years.

It seems very likely that the Brazil's target will be reached. Last year, the country announced the lowest deforestation rate to date – 650,000 hectares. Nevertheless, it is Rousseff's administration that will need to guarantee that destruction in the Amazon will not return and that it will drop by a further 300,000 hectares, as stated by the national target.

While Lula emphasised police tactics, Rousseff will have to deal with the pressures that are increasing within the national congress. The group of congressman defending the interests of the agricultural sector – the bancada ruralista – is asking for changes in one of the most important environmental laws of the country, the forest code.

Join these pressures coming from the congress with the eagerness of the government to create large infrastructure in the Amazon and you understand the bitterness of the greens in Brazil. The question is: will it really be possible for the new president to fulfil her pledge of making the country grow without destroying the environment?

Gustavo Faleiros is the editor of Brazilian environmental news agency O Eco

• This article was changed on 1 February to read 60,000 hectares