They planned to travel about 36 hours upriver to the city of Macapá, Mr. Brandle said. But around 7 p.m. local time on Sunday, the barge was allegedly attacked near Breves by pirates, who brought the vessel and accompanying tugboat to an area known as Porto dos Dias, according to a statement from the Pará state police, citing eyewitness reports. There, the attackers took goods off the barge and abandoned the vessels, leaving the passengers and crew stranded, police said.

Upon arriving at the scene, the police said the Harteaus were no longer on the boat.