Agents have been paying particular attention to the rafters of international bridges in El Paso since last year when a similarly crude system for smuggling drugs was discovered.
"You can't knock the ingenuity. It's there," Border Patrol spokesman Doug Mosier said.
The man told agents that smugglers in Mexico had arranged to get a group of people across the river using the cart, Mosier said. It's unclear how many people may have used it previously.
Rafael Ernesto Corvalan Herrera, 33, was arrested Sunday afternoon and faces a federal felony charge of illegally entering the country after being deported. He is a registered sex offender in Florida.
Corvalan is being held without bond at the El Paso County jail, where records do not show if he has a lawyer.
According to law enforcement records in Florida, Corvalan was deported after February 2003 convictions for sexual battery using threats of force or violence, and false imprisonment.