Migration toward the United States through the dangerous jungle passage known as the Darién Gap has been halted, at least temporarily, following the arrest of two boat captains working for companies that play an essential role in ferrying migrants to the jungle.

Boat companies suspended migrant crossings from two northern Colombia towns, Necoclí and Turbo, to the entrance of the Darién forest, according to the mayor of Necoclí, leaving roughly 3,000 migrants stranded in those communities.

The Colombian law enforcement action in the region is sure to be watched closely by U.S. officials: The Biden administration has been pressuring Colombia for months to try harder to stop people from using the Darién as a path to the United States.

The boat route is the main way into the Darién Gap, a strip of land linking South and North America that was once rarely traversed but has emerged in recent years as one of the hemisphere’s most important and busiest migration routes.

Nearly a million people have crossed the Darién since 2021, according to the authorities at the end of the route in Panama, helping to fuel an immigration crisis in the United States.