A team of biologists, vets and fishermen temporarily captured rare freshwater dolphins in the Amazon this week to study their health in hopes of avoiding a repeat of the deaths of hundreds of the mammals last year due to a severe drought.

The dolphins, that are in danger of extinction, were brought ashore for blood tests and other examinations and returned to Lake Tefé in the Amazon basin as soon as the researchers had finished their work.

Fishermen were careful not to injure an adult female dolphin during capture and kept her close to her young offspring to avoid stressing the animals.

"She relaxed and we could do all the tests. She appeared in good health," said project leader Miriam Marmontel of the Mamirauá Institute for Sustainable Development, which planned the expedition to temporarily capture up to 20 dolphins.

The work included removing a sample for a biopsy to see whether there were contaminants in her blubber, and the placing of a microchip for future identification. Satellite tags to follow the behavior the dolphins, the depth they swims at and check water temperatures remotely had not been attached yet.

In a grim fallout from the longest drought in the Amazon rainforest's recorded history last year, induced in part by climate change, the carcasses of more than 200 river dolphins were found floating on Lake Tefé, which is formed by a tributary of the Amazon River.

Low river levels during the drought heated the water to temperatures that were intolerable for the dolphins, researchers say. Thousands of fish also died in Amazon waterways due to a lack of oxygen in the water.