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A burst of pink appears on the muddy surface of the Amazon River as scientists and vets, standing waist-deep in the warm water, carefully maneuver a mesh net around a group of river dolphins. They pull the net tighter with every pass, and a shower of silver fish shines under the intense sunlight as they jump to flee the net.

As the team pulls a dolphin onto a boat, it struggles while water flows from its sides marked with pink spots, and the crew swiftly takes it to the sandy riverbank where excited researchers place it on a mat. They have 15 minutes—the maximum time a dolphin can remain out of water safely—to finish their tasks.

Fernando Trujillo, a marine biologist overseeing the operation, crouches near the creature’s head, covering its eye with a tiny piece of fabric so it remains unaware of the proceedings. He places his hand softly on the animal and talks in a quiet voice.

They have never experienced the touch of a hand. We attempt to soothe them,” said Trujillo, wearing a pink dolphin bandana. “Removing a dolphin from the water is akin to an abduction.

One individual monitors the dolphin’s breathing. Another applies moisture to its skin using a sponge, while the rest carry out various medical examinations that will reveal the extent of mercury present in the Amazon’s most elegant predators.

The danger of mercury spreads throughout the Amazon’s food chain

Trujillo oversees the Omacha Foundation, an environmental organization dedicated to protecting aquatic life and river habitats, and supervises health assessments of river dolphins. This meticulous process involves skilled fishermen, vets, and community members, requiring extensive preparation and occurring just a few times annually.

We collect blood and tissue samples to evaluate mercury levels,” Trujillo said to The Associated Press from the Colombian riverside town of Puerto Narino. “In essence, we are using dolphins as indicators of the river’s well-being.

Mercury pollution primarily stems from unauthorized gold mining, an expanding sector throughout the Amazon Basin, and deforestation that leads to mercury naturally present in the soil being washed into rivers.

Miners employ mercury to extract gold from sediment, then dispose of the sludge back into rivers, allowing it to contaminate fish that are consumed by both humans and dolphins. Increasing global gold prices have driven a surge in mining activities, leading to higher levels of mercury pollution in isolated waterways.

Mercury can harm the brain, kidneys, lungs, and immune system, leading to mood changes, memory issues, and muscle weakness in individuals, as stated by the World Health Organization and the U.S. Environmental Protection Agency. Pregnant women and young children are particularly vulnerable, with exposure during pregnancy associated with developmental delays and impaired cognitive abilities.

The highest amount any living organism should be exposed to is 1 milligram per kilogram,” Trujillo stated. “In this case, we are observing 20 to 30 times that level.

In earlier years, his team discovered 16 to 18 milligrams of mercury per kilogram in dolphins, which can experience similar neurological harm, organ issues, and other health problems as humans. In Colombia’s Orinoco River, mercury levels in certain dolphins have climbed as high as 42, according to scientists who describe these as some of the highest recorded in the species.

Trujillo mentioned that it’s challenging to demonstrate that the toxin is directly causing the death of dolphins. Additional research is being conducted, he stated, pointing out that “any mammal exposed to a significant level of mercury will perish.”

When Trujillo and his team analyzed their own blood three years back, the findings revealed more than 36 times the acceptable threshold — 36.4 milligrams per kilogram — a concentration he links to many years spent in regions contaminated with mercury and a diet rich in fish. With medical support, his levels have decreased to approximately 7 milligrams.

Mercury is a hidden threat until it accumulates to a dangerous level, after which it begins to impact the central nervous system,” Trujillo said to AP following his team’s successful capture and testing of four pink dolphins. “We are already observing signs of its effects in Indigenous communities.

Numerous scientific studies and reports—such as those conducted by the International Pollutants Elimination Network and university researchers—have revealed significant mercury exposure among Indigenous populations throughout the Amazon, including in Brazil, Peru, Colombia, Suriname, and Bolivia. Analysis of hair samples indicated levels far exceeding the World Health Organization’s recommended limit of 1 part per million, with one community in Colombia recording over 22 milligrams per kilogram.

Pink dolphin numbers in this section of the Amazon have significantly decreased, according to Trujillo’s research, which indicates a 52% reduction in pink dolphins and a 34% decrease in gray river dolphins, a separate species, over recent years. The International Union for Conservation of Nature classified the pink dolphin as endangered in 2018. Trujillo mentioned that precise figures for the Amazon are not available, but his group estimates the population ranges between 30,000 and 45,000 throughout the basin.

Pink river dolphins are also at risk due to overfishing, unintended capture in fishing gear, increased boat movement, destruction of their environment, and extended dry periods.

Colombia claims it is addressing illegal mining and mercury contamination. The country prohibited the use of mercury in mining in 2018, joined the Minamata Convention designed to cut down on mercury in the environment, and presented an action plan in 2024. Officials mention collaborative operations with Brazil and recent enforcement actions, yet watchdogs argue that efforts are inconsistent and illegal mining continues throughout large parts of the nation.

Other Amazon countries state they are increasing their efforts. Brazil has initiated raids and imposed restrictions on satellite internet utilized by illegal gold-mining camps that employ mercury, with the goal of disrupting logistics and supply chains. Peru recently confiscated a record 4 tons of smuggled mercury. Ecuador, Suriname, and Guyana have submitted action plans to reduce mercury usage in small-scale gold mining.

A careful procedure to evaluate dolphins in a secure manner

The dolphin testing initiative is led by José “Mariano” Rangel, a compelling ex-fisherman from Venezuela. He takes the lead when it’s time to bring the animals — which can reach up to 160 kilograms (approximately 353 pounds) — into the small boats. This is a moment that can result in a painful strike to the jaw as the dolphins struggle to escape.

“The hardest aspect of the captures is containing the dolphins,” Rangel stated.

A mobile ultrasound device examines the lungs, heart, and other essential organs for illness. The group looks for breathing issues, internal wounds, and indications of reproduction, take pictures of the animals’ skin and scars, swab the blowholes and genital areas for bacterial samples, and gather tissue for mercury analysis. Microchips are inserted so scientists can recognize each animal and prevent repeating tests.

Omacha has documented antimicrobial resistance—where bacteria are unaffected by standard treatments—and breathing-related health issues. They have also discovered potential new diseases, like the papilloma virus, which may present dangers to both dolphins and people.

Following an extended morning spent transporting and examining dolphins, the researchers go back to a lab in Puerto Narino adorned with images of dolphins and manatees, along with the skeletons and skulls of dolphins and other creatures. They analyze certain samples, get others ready for shipment to bigger centers, and conclude their day by mending nets and restocking supplies to repeat the process at sunrise.

For Trujillo, every capture, scan, and blood test is a component of a broader struggle.

“We are one step closer to being critically endangered and then facing extinction,” Trujillo stated.