A flash of pink breaks the muddy surface of the Amazon River as scientists and veterinarians, waist-deep in the warm current, patiently work a mesh net around a pod of river dolphins.

They draw it tighter with each pass, and a spray of silver fish glistens under the harsh sun as they leap to escape the net.

When the team hauls a dolphin into a boat, it thrashes as water streams from its pink-speckled sides and the crew quickly ferries it to the sandy riverbank where adrenaline-charged researchers lift it onto a mat.

They have 15 minutes — the limit for how long a dolphin can safely be out of the water — to complete their work.

Fernando Trujillo, a marine biologist leading the effort, stays by the animal’s head, shielding its eye with a small cloth so it can’t see what’s happening.

He rests his hand gently on the animal and speaks in low tones.

“Taking a dolphin out of the water, it’s a kind of abduction.” said Trujillo. "We want to do this quickly, and we are monitoring that the animal is comfortable, and we return it very quickly to the river."

One person counts the dolphin's breaths.

Another wets its skin with a sponge while the others carry out multiple medical tests that will help show how much mercury is coursing through the Amazon’s most graceful predators.

Mercury threat spreads through the Amazon food chain. Trujillo directs the Omacha Foundation, a Colombian conservation group focused on aquatic wildlife and river ecosystems, and leads health evaluations of river dolphins.

It's a painstaking operation involving experienced fishermen, veterinarians and locals that take months of planning and are done only a couple times each year.

Mercury contamination comes from two main sources, Trujillo said.

Illegal gold mining upstream — a growing industry across the Amazon Basin — and forest clearing that washes mercury that naturally occurs in soil into waterways.

The miners use mercury to separate gold from sediment, then dump the sludge back into rivers, where it enters fish eaten by people and dolphins.

Rising global gold prices have fueled a mining boom and mercury pollution in remote waterways has increased.

Mercury can damage the brain, kidneys, lungs and immune system and cause mood swings, memory loss and muscle weakness in adults, according to the World Health Organization and the U.S. Environmental Protection Agency.

In previous years, his team found 16 to 18 milligrams per kilogram of mercury in dolphins, which can suffer the same neurological damage, organ damage, and other problems, including death, as humans.

In Colombia’s Orinoco River, levels in some dolphins have reached as high as 42, levels scientists say are among the most extreme ever recorded in the species.

Colombia says it is tackling illegal mining and mercury pollution. It banned mercury use in mining in 2018, ratified the Minamata Convention and submitted a national action plan in 2024.

Brazil has tightened raids and moved to restrict satellite internet used by illegal gold-mining camps that use mercury, aiming to disrupt logistics and supply lines.

Peru recently seized a record 4 tons of smuggled mercury. Ecuador, Suriname and Guyana have filed national action plans to cut mercury use in small-scale gold mining.

A portable ultrasound machine scans the dolphins' lungs, heart and other vital organs for disease.

Veterinarians check for respiratory problems, internal injuries and signs of reproduction, while other team members photograph the animals' skin and scars, swab blowholes and genital openings for bacterial cultures, and collect tissue for mercury testing.

Microchips are implanted so researchers can identify each animal and avoid duplicating tests.

Omacha has recorded antimicrobial resistance — bacteria that can’t be killed by common medicines — and respiratory problems.

They have also identified possible emerging diseases, such as papilloma virus, that could pose risks to both dolphins and humans.

After a long morning hauling and testing dolphins, the scientists return to a laboratory in Puerto Narino that's covered with posters of dolphins and manatees and the bones and skulls of dolphins and other animals.

They test some samples, prepare others to send to larger facilities and end their day repairing nets and refilling kits to do it all again at dawn.

AP Video shot by Cesar Olmos

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