It was envisioned to be the Mississippi River of South America.

The Paraguay-Paraná waterway runs about 2,100 miles, connects at least 150 ports in five countries and serves as the most important commercial river route on the continent. In 1992, the five countries — Brazil, Bolivia, Paraguay, Argentina and Uruguay — agreed to establish the two natural rivers, which meet at the Paraguay-Argentina border, as a transit route for goods, dredging them to allow commercial traffic. Every year, thousands of container ships, barges and other vessels use the waterway’s brown, bustling waters to carry millions of tons of cargo south to Argentina and from there across the Atlantic.

But this crucial artery has a new function. It has become a primary route for shipping record amounts of cocaine to Europe.

The explosion in the global container shipping business has allowed drug traffickers to take advantage of a waterway that just years ago would have seemed illogical — heading south, instead of north, from airstrips in Bolivia to ports in Paraguay to Argentina’s Río de la Plata estuary.

It now feeds Europe’s and the world’s growing appetite for cocaine. Since the pandemic, some of the largest drug busts in Europe have arrived on containers that first traveled down this river. Cocaine seizures linked to the Paraguay-Paraná system shot up fivefold between 2010 and 2021, according to the U.N. Office on Drugs and Crime (UNODC).

To take one example: Last year, after departing Asunción, a ship with more than 12 tons of cocaine slipped undetected down the Paraguay River. One of its containers, carrying black sesame seeds to conceal the drugs, left the Paraguayan capital in May 2023 and traveled south to Uruguay, where it was loaded onto a different ship to Europe.

The drugs were found in the port of Hamburg in early July. It was the largest seizure outside South America in all of 2023.

Nine days before the container of sesame seeds was loaded in the port in Asunción, Paraguayan officials had thrown a parade to celebrate the arrival of five new scanners, four of them donated by Taiwan and made in the United States. “With this powerful fleet of high-tech equipment,” the country’s customs officials said in a post. “Paraguay is no longer a river transit country for organized crime.”

The massive seizure in Hamburg hit the Paraguayan government like “a bucket of cold water,” one government official said, speaking on the condition of anonymity because he was not authorized to discuss the case. “It was a huge embarrassment.”

High-end technology, officials realized, was not a panacea.

“It’s the eternal game of cat and mouse,” said Nicolás Benza, head of UNODC’s container program for the Southern Cone. “They have unlimited resources, while our resources are limited.”

A new cocaine transit hub

For generations, drug smugglers focused their business on the American consumer, trafficking cocaine from Colombia to Central America and the United States. The Brazilian port of Santos often served as an alternative departure point from South America. But today, as the cocaine industry has boomed and as security officials have cracked down on traditionally vulnerable ports, criminal groups have carved out new routes and new markets.

Paraguay became an appealing transit point. It’s one of the world’s largest exporters of soybeans, beef and organic sugar. A landlocked country of less than 7 million people, it now boasts the third-largest barge fleet in the world, behind only the United States and China.

Just this year, about 78,000 containers have left Paraguayan ports on their way south to Argentina or Uruguay and across the Atlantic, according to customs figures.

But the country’s law enforcement was not built to combat transnational organized crime. Paraguay, unlike its neighbors, has virtually no air radars. This makes it easy for traffickers in Bolivia to fly drugs — cocaine produced in either Colombia, Peru or Bolivia — onto illegal airstrips in the northern part of Paraguay, one of the most sparsely inhabited areas on the continent.

From there, the drugs are taken by truck to warehouses, where they are concealed in containers bound for the river.

“The evolution of organized crime has been faster than the evolution of the security forces,” said Oscar Chamorro, head of Paraguay’s coast guard.

Every container that leaves a Paraguay port is now required to pass through a scanner. But drug traffickers are increasingly finding their way around the technology, investigators said, mixing cocaine in liquids, powders and other materials to disguise the substance. In June, Paraguayan authorities found more than four tons of cocaine stashed inside bags of sugar in a container in Asunción, bound for Antwerp, Belgium. It had passed through a scanner undetected.

“We have our doors wide open,” said Deny Yoon Pak, the prosecutor overseeing the sesame case. “How much cargo has been shipped and we had no idea?”

Earlier this month, Paraguay’s antidrug agency announced it would be halting cooperation with the United States, jeopardizing some of the most important investigations into cocaine smuggling in the country. One of those cases involves the search for Sebastián Marset, the fugitive drug kingpin who hid as a professional soccer player and is believed to control much of the trafficking down the Paraguay river. Some former Paraguayan officials argued the move was an attempt to protect top Paraguayan politicians with ties to drug trafficking.

Following a story in The Washington Post that reported on the planned end to cooperation, the Paraguayan government reversed its decision, saying it plans to strengthen collaboration with the U.S. Drug Enforcement Administration.

A ship departs after a final search

Night fell over the port just south of Asunción as a crane lifted one container after another, slowly lowering each one onto the Josamo ship as it prepared to depart.

“Not yet, not yet!” shouted one of the crew members, wagging his finger and waving for the crane operator to keep going, then stop, before the container landed squarely in a spot below, with a loud bang.

In just a few hours, the captain and crew of the Josamo would begin their journey south to Uruguay, carrying containers that would be reloaded onto larger vessels heading to Europe and around the world.

The crew had never discovered any cocaine on board. Still, the captain, as he always does, instructed one of his crew members, this time Hector Medina, 37, to do a final round of checks throughout the ship. Carrying a flashlight, Medina crawled through dark tunnels and peered into cracks between containers, searching for hints of contraband. (The owner of the ship allowed Post journalists to travel partway down the waterway on the Josamo.)

A gateway to the Atlantic

The narrow river was lined by marshes and farmland, sprinkled with occasional horses and cows. There were few lights. The following day, one river flowed into another — the Paraguay becoming the Paraná — and the Josamo reached Argentina.

The ship would pass by the industrial city of Rosario, the hometown of soccer great Lionel Messi and the birthplace of Marxist revolutionary Che Guevara. The third-largest city in Argentina, it also ranks among the top agricultural ports in the world.