In it are three gold and diamond buyers, armed with weighing scales, magnifying glasses and rucksacks stuffed with cash. They stop off every few minutes at many of the illegal mines that line the river and scar the jungle.
Despite appearances, this is a prosperous business. Standing at the edge of the pit, Jesús López, 45, says that he earns $2,000 in an average week.
"I make this sacrifice for my children,” he says.
In Santa Elena, the nearest town to these mines, one buyer, with a gun in his holster and a desk littered with gems, explains the illegal business.
The diamonds he purchases will probably end up in trading centres such as Tel Aviv, Antwerp, London and New York after being smuggled into neighbouring Guyana for the obtention of falsified papers.
The route flouts the Kimberley Process, an international pact agreed in 2003 to curtail the diamond smuggling that was fuelling civil wars in Africa - the trade in so-called "blood diamonds."