Mining dredges return to Amazon River’s main tributary, months after crackdown

In 2021, an army of dredges equipped to churn up the riverbed in search of gold invaded the largest tributary of the Amazon River in Brazil. The structures lined up like walls along the Madeira River, which has a history of illegal mining. Yet that moment was historic in its own right for the sheer scale of the activity and its location close to the Amazonas state capital, Manaus, away from the traditional areas of exploitation deeper in the rainforest.

Brazil at the time was headed by Jair Bolsonaro, a right-wing president who openly supported illegal gold miners, known locally as garimpeiros, operating in the Amazon. Things started to change in 2023, when Bolsonaro’s successor, Luiz Inácio Lula da Silva, resumed operations on the ground against illegal mining and created tougher rules for gold trading in Brazil.

The Lula government’s first major raid on gold miners took place in the Yanomami Indigenous Territory, in Roraima state, where a humanitarian crisis wrought by the massive influx of garimpeiros made international headlines. A task force expelled most of the illegal miners, and health professionals went in to treat hundreds of cases of malaria and malnutrition among the Indigenous population.

In August 2024, federal forces concentrated their efforts on the Madeira River, destroying 459 dredges, 100 of them inside Indigenous territories.

Only five months later, however, the dredges are back, as shown by a report published in early February by Greenpeace.

Using satellite imagery, the organization detected a new cluster of 130 dredges moving from Jan. 10 to 22 in the stretch between the Amazonas municipalities of Novo Aripuanã and Humaitá. “They are circulating in the region even after the various police operations that have taken place in recent years,” Jorge Dantas, Greenpeace Brazil’s spokesperson, told Mongabay. “This shows that the wheels that keep this illegal activity working continue to turn.”

 Brazil’s federal environmental agency, IBAMA, told Mongabay by email that a total of 1,222 dredges were destroyed from 2023 to 2024 in Amazonas state, 800 of them in the Madeira River. “In 2025, actions to combat illegal mining will continue throughout the Amazon region, in order to disrupt the logistics of criminal activity linked to mining in the region,” the agency said in the statement.

Originating in the Bolivian Andes, the Madeira River is key to the Amazon Basin, both environmentally and economically. It’s home to the region’s largest fish diversity, accounting for 60% of all described species. At the same time, 10% of the commodities transported by waterway in Brazil flows through the Madeira. Despite its importance, the river has long been impacted by illegal mining, deforestation, and two major hydropower plants that have affected the river’s hydrological cycle and fish migratory patterns. “This is not just any river. It makes life possible for a number of populations and cities,” Dantas said.

The return of the dredges to the Madeira is part of a broader dynamic, he added, in which garimpeiros are migrating to new sites as the traditional mining areas of the Amazon, like the Yanomami and the Munduruku Indigenous territories, come under intense monitoring. “The police arrive in one place, the people leave, but naturally they go to another place where there is less surveillance,” Dantas said.

As Mongabay reported in 2024, gold miners are resisting Lula’s crackdown.

Among their new targets are conservation areas. In September and October 2024, garimpeiros converted an area the size of New York City’s Central Park into illegal mines in 15 protected areas monitored by Greenpeace.

Luiz Jardim Wanderley, a geography professor at Fluminense Federal University in Rio de Janeiro state, follows data on conflicts related to illegal gold mines, or garimpos, in the Amazon. He said he’s also observed the migration of these conflicts to new hotspots in Amazonas and Acre states. In Maués municipality, in Amazonas, the Federal Police found a network of underground gold mines where garimpeiros were working in conditions analogous to slavery. The goal was to go unnoticed by the satellite imageries.

“In the last year, there has been a reduction in mining-related conflicts, but the distribution of these conflicts across the territory has increased. Conflicts have spread to different locations,” Wanderley said.

The dredges are equipped with a metallic arm known as a “pineapple,” which stirs up the riverbed. Large hoses bring the mud up to a conveyor belt, where mercury is used to separate gold from other sediments. The waste is then thrown back into the river, contaminating the water consumed by traditional communities. A recent study showed high levels of mercury in the Madeira River.

Despite their severe impact, it’s proved difficult for the authorities to rein in the dredging operations. Unlike mining on riverbanks, which leave craters in the middle of the forest and are easily detectable by satellite imagery, dredges often go unnoticed. “They are the most dynamic part of the gold production chain. The dredge is here today, somewhere else tomorrow,” Dantas said.

The latest report on the Madeira River dredges is the first test of a new technology developed by Greenpeace to improve the detection of these structures. “This is the first product of a new methodology that allows us to take a more detailed look at what happens in the Amazon Rivers,” Dantas said.

Banner image: The mining dredges are equipped with a metallic arm that stirs up the riverbed in search of gold. Image courtesy by Bruno Kelly/Greenpeace. 

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