The race to find out what killed hundreds of pink dolphins in the Amazon – in pictures

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Scientists are trying to establish whether global heating caused the deaths of the rare river dolphins last year, before temperatures start to rise again

Bruno Kelly

Main image: Field researchers from the Mamirauá Institute for Sustainable Development capture a rare Amazon river dolphin, or pink river dolphin, during an expedition to Lake Tefé in the Amazon basin. The scientists want to assess their health and install GPS tags after 300 of the animals died in drought last year. Photograph: Bruno Kelly/Reuters

  • Residents of the Solimões River region in Amazonas state carry emergency supplies of drinking water last October. The longest drought in the Amazon rainforest’s recorded history hit the area around Lake Tefé last year, and scientists fear a recurrence in 2024.
    People carry food and containers of drinking water across an arid landscape

  • The carcasses of hundreds of river dolphins were found last year on Lake Tefé, which is formed by a tributary of the Amazon River.
    A boat full of people observe the washed-up body of a dead dolphin

  • A pink dolphin is pulled from Lake Tefé as part of the research being conducted this month, led by the Mamirauá Institute for Sustainable Development. The animals, which get their name from their often striking pink colour, are a unique freshwater species found only in the rivers of South America and one of a handful of freshwater dolphin species left in the world. Slow reproductive cycles make them especially vulnerable to threats.
    A group of researchers wading in a lake hold the body of a dolphin

  • Biological samples are taken to check how the dolphins are responding to heat. Up to 20 of the species, which are in danger of extinction, were brought ashore for blood tests and other examinations before being returned to the lake.
    Scientists clasp the pink tail of a dolphin to extract a sample

  • Low river levels during last year’s drought meant the water heated to temperatures that were likely intolerable for the dolphins, researchers say – but they may have also been affected by toxins or pollutants. Thousands of fish also died in Amazon waterways due to a lack of oxygen in the water.
    A scientist wearing blue gloves holds the pink tail of an Amazon river dolphin

  • A female dolphin is carefully tagged with a microchip before being returned to the water. ‘She relaxed and we could do all the tests. She appeared in good health,’ says Miriam Marmontel, the Mamirauá Institute’s project leader.
    The eye of a restrained river dolphin on which scientists are conducting tests

  • Scientists conduct tests including a biopsy to check for contaminants in a dolphin’s blubber. Researchers say they hope to establish what caused last year’s deaths before this season’s drought sets in, as the Amazon dry season begins.
    Scientists hold a medical instrument to the side of a dolphin

  • ‘We aim to learn more about the health of the dolphins at a time when water levels begin to go down and temperatures start to rise, so we can identify the changes and know whether they are due to higher temperatures or a toxin or pollutant in the water,’ Marmontel says.
    Scientists using medical equipment take a sample from the tail of a dolphin

  • The researchers want to be able to react quickly if drought again threatens the rare dolphins.
    A group of researchers gathered around a table on board a boat with notes and samples

  • In January, scientists concluded that the record-breaking drought was made 30 times more likely by global heating.
    A field researcher looks at their phone

  • Most of the dolphins that perished last year were in Lake Tefé. The lake’s waters reached 40.9C during the 2023 drought, more than 10 degrees higher than the average for the time of the year.
    A drone view shows Amazon river dolphins in a lake
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