A British adventurer who was canoeing alone in the Amazon may have been snatched by pirates, according to Brazilian police.
The 43-year-old woman, who has not been named, was attempting a 6435km solo journey from Peru to Brazil.
She disappeared last week while travelling through a stretch of river which is part of a drugs trafficking route and known for frequent pirate attacks.
Her canoe and belongings were later found on sandbanks on the side of the Solimões River in Brazil's northern jungle state of Amazonas.
Ivo Martins, the state's civil police chief, said: "There are various lines of inquiry. She could have been killed by drugs traffickers, or attacked by pirates, but she could also have been attacked by an animal, or just got lost".
Police said the canoeist got into difficulty last Thursday when she activated an emergency locator device when she was between the towns of Codajas and Coari, 240km west of Manaus.
The Brazilian Navy said 60 personnel were continuing their search for the woman, who they described as a "professional sportswoman who has experience in navigation".
"The information that we have is that her objective was to follow the Amazon River all the way to its mouth," said Paulo Veiga, the captain of the District Naval Command in Manaus.
Martins indicated the investigation had found "consistent information" from local eyewitnesses, and said police were working with the possibility the woman is still alive.
He added that the search efforts will continue until "all possibilities of finding the English woman have been exhausted".
The state's previous civil police chief, Thyago Garcez, disappeared in December in almost exactly the same remote stretch of the Solimoes River after an incident involving drug traffickers. His body has never been found.