At Least 125 River Dolphins Have Died Amid Drought and Heat in Brazilian Amazon

At least 125 river dolphins have died in a Brazilian lake in recent weeks, likely due to a combination of drought and unusually high water temperatures.

The creatures’ carcasses began floating in Lake Tefé and washing ashore on September 23, reports the New York Times’ Ana Ionova and Livia Albeck-Ripka. The body of water is located near the town of Tefé, a remote community in Brazil’s Amazonas state.

Scientists are still trying to determine the cause of the deaths, which span two species—pink river dolphins (Inia geoffrensis) and tucuxi river dolphins (Sotalia fluviatilis). They’re investigating whether a disease or toxin made its way into the water, however, they suspect the heat is to blame.

At the end of September, the water of Lake Tefé reached 102 degrees Fahrenheit (39 degrees Celsius), which is much warmer than normal. One researcher investigating the deaths described the warm water as “soup,” per the New York Times.

When the lake becomes too hot, dolphins can get disoriented. They end up swimming around in circles, and eventually, they die because of a lack of oxygen, reports the Washington Post’s Diana Durán.

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Dozens of researchers, veterinarians and conservationists have stepped in to provide help. Some are retrieving dolphin carcasses to get tissue samples for analysis, while others are relocating sick dolphins into artificial pools for observation and rehabilitation.

It may be a while before scientists can officially determine what killed the dolphins, however. Lake Tefé is far from big cities with laboratories—it’s located some 2,000 miles from Rio de Janeiro and 1,850 miles from São Paulo, for example. The drought has also made transportation within the remote region even more difficult, as some smaller waterways and tributaries of the Amazon River have dried up, and the only way to get around would typically be by boat.

This has also cut off some local communities from supplies of drinking water, gas and food. As such, the state of Amazonas has declared a state of emergency for many of its municipalities, and the Brazilian government set up a task force to provide emergency aid, per Reuters.

“Many communities are becoming isolated, without access to good quality water, without access to the river, which is their main means of transportation,” says Ayan Fleischmann, geospatial coordinator at the nonprofit Mamirauá Institute for Sustainable Development, to Mauricio Savarese of the Associated Press (AP).

Amazon river dolphins, also known as pink river dolphins, can grow up to nine feet long and weigh more than 350 pounds, per the World Wildlife Fund. They live only in freshwater, and in addition to Brazil, they inhabit the river basins of Bolivia, Venezuela, Guyana, Colombia, Peru and Ecuador.

The International Union for Conservation of Nature lists the species as endangered and reports that its numbers are shrinking. The dolphins are susceptible to numerous threats, ranging from industrial and agricultural pollution to drilling for oil and gas.

Pink river dolphins are a source of tourism income for some local communities, which call them “boto” or “bufeo,” per the New York Times. They are part of Amazonian legends and stories, including one in which the dolphins turn into handsome men to seduce young women. The animals’ well-being is thought to be an indicator of the health of the river ecosystem.

Meteorologists blame El Niño for the region’s hot, dry weather and say the conditions could persist for months, writes Thiago Alves for Brazil Reports. If that’s the case, researchers fear even more dolphins could die. An estimated 1,400 river dolphins lived in Lake Tefé before the recent deaths, per the AP, and additional losses could be a blow to the slow-to-reproduce population.

Thousands of fish have also died off, and their carcasses are contaminating the drinking water, per Reuters.

“The past month in Tefé has seemed like a science-fiction climate change scenario,” says Daniel Tregidgo, a British researcher who lives in the region, to the Guardian’s Jonathan Watts. “To know that one [dolphin] has died is sad, but to see piles of carcasses, knowing that this drought has killed over 100, is a tragedy.”

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Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.