Amazon fish show severe deformities nearly decade after brazil’s controversial belo monte dam began operations

Nearly ten years after Brazil’s massive Belo Monte hydroelectric dam began operating on the Xingu River in the Amazon, researchers are documenting alarming deformities in local fish populations that suggest long-term ecological damage to this critical waterway.

The 11.2-gigawatt Belo Monte plant, which became operational in 2016, diverted the course of the Xingu River and dramatically reduced water flow through a 130-kilometer stretch known as the Volta Grande do Xingu, or “Large Curve.” Almost immediately after the dam’s turbines started running, researcher Jansen Zuanon observed disturbing changes in the river’s fish populations. During early monitoring visits with federal prosecutors and environmental observers, Zuanon found spotted sorubim fish exhibiting severe malnutrition, with sunken eyes, wounds, missing teeth, and heavy parasite loads. He described them as “zombie fish, dying little by little.”

The environmental impacts have persisted and worsened over time. In 2025, the same monitoring team documented new deformities in silver croakers, finding specimens with abnormally squat, oval bodies instead of their characteristic elongated shape—clear evidence of spinal deformities. These physical changes indicate that the dam’s disruption of the river’s natural flow patterns continues to devastate aquatic ecosystems nearly a decade later.

The findings represent a troubling validation of environmental groups’ long-standing concerns about the Belo Monte project, one of Brazil’s most controversial infrastructure developments. The documented fish deformities provide concrete evidence of the dam’s ongoing ecological toll on one of the Amazon’s most important tributaries and the communities that depend on it.