For 10 days, the people of Tef have awakened to a terrible sight: the carcasses of pink river dolphins floating in Lake Tef, food for circling buzzards.
More than 150 of the beloved, endangered animals have died in this lake in Brazil's Amazonas state, alarming scientists and wildlife advocates. The cause is unknown, but scientists say the likeliest culprit is extreme heat and drought, possibly linked to climate change and the El Nio phenomenon.
The water temperature in Lake Tef has reached 102 degrees Fahrenheit - 59 degrees more than the average for a body of water in the Amazon - and water levels have fallen dramatically.
When the water is that warm, dolphins become disoriented, said Claudia Sacramento, head of the Environmental Emergencies Division at the governmental Chico Mendes Institute for Biodiversity Conservation. The loss of oxygen triggers an increase in their cell metabolism, and they die of asphyxia.
"It is common for communities to run into a dead dolphin or two at some point," Sacramento said. "Usually they're just old or sick. But we had never seen something like this before."
Nor, it is believed, has any other country in the Amazon.
Authorities are also studying whether a biotoxin or virus might be causing the die-off. Hundreds of fish in the Amazon also have died recently.
But researchers believe the simplest explanation is heat and drought. With El Nio and record-breaking heat in Brazil and other parts of South America expected to continue in the coming months, they fear, more dolphins could die.
"We're getting ready for the worst," said Adriana Colosio, a veterinarian from the Humpback Whale Institute who is in Tef helping examine dolphin carcasses.
At least 10 veterinarians have volunteered to perform necropsies and collect samples to be processed by specialized laboratories in So Paulo and Rio de Janeiro.
Authorities say they need lab results to better understand the cause of the deaths.
"That's the question everyone wants to solve: What's happening with these animals?" Colosio said.
But the effort faces challenges. One is finding carcasses in "good condition" for taking samples; in the water and heat, the dolphins' remains decompose rapidly.
Another challenge is keeping the samples frozen while transporting them for analysis. Tef, a remote city of 60,000, is around 1,850 miles from So Paulo and 2,000 from Rio. The lack of regularly scheduled direct flights and strict regulations on transferring biological matter make it unclear when they will reach the labs.
Two teams totaling 48 people are working in the lake - one to monitor and rehabilitate animals, the other to pull carcasses out. The Mamirau Institute for Sustainable Development has rented a house on the lake to help rescue dolphins.
Yurasi Briceo, director of the Sotalia Project, an organization in Venezuela that researches and conserves aquatic mammals there, called the dolphin deaths in Brazil "a catastrophe."
"No country in the region is prepared to face a situation like this," she said.
Briceo said "it's only a matter of time" before other rivers in the Amazon suffer similar die-offs: "Global changes are real."
Mariana Paschoalini Frias, a conservation specialist with the World Wildlife Fund in Brazil, fears Lake Tef could lose 10 percent of its population of dolphins. If the deaths continue, she said, "the population will be in danger."
Heat and historic drought are wreaking havoc throughout South America. Scientists in Venezuela and Colombia are watching the rivers of the Orinoco and Amazon basins carefully. Lake Titicaca, the highest navigable lake in the world, is drying out for want of rain. Sea wolves in Ecuador are starving; warm surface waters are killing their food.
At least 30 manatees in Pantanos de Centla nature reserve, home to Mexico's largest manatee population, have died this year, according to Azcarm, an association of zoos, breeding centers and aquariums. At least 139 died from 2018 to 2022. A study sponsored by the National Commission of Protected Natural Areas last year blamed "diverse human activities," including the construction of petrochemical infrastructure.
"The area is way too polluted," said Ernesto Zazueta, Azcarm's president. "The drought and the heat waves are a trigger. This year it has barely rained."
Pink river dolphins, which some Indigenous communities consider sacred, are emblems and mascots of the region. They are also canaries in the coal mine - their failing health can reveal threats to the larger ecosystem.
"We're provoking this ourselves," Colosio said. "If something bad happens to the dolphins, we are next."
