The Rio Grande under Trump

Now, the agents look out on an empty landscape. Foot paths up from the water have started to disappear under growing brush, with only the stray baby shoe or toothbrush serving as reminders of that migrant flood.

The reason for the change, the agents say, is a perception in Mexico and Central America that President Donald Trump has ended the practice known as "catch-and-release," in which immigrants caught in the United States without proper documents were released to live free, often for years, as their cases ran through the court system.

Now, would-be border violators know "they'll be detained and then turned right back around," said one of the two agents, Marlene Castro. "It's not worth it anymore," she said.

Castro was simply echoing her boss, Homeland Security Secretary John Kelly, who said on a visit to El Paso, Texas in April, “We have ended dangerous catch-and-release enforcement policies.”

But immigration attorneys, government statistics and even some officials from U.S. Immigration and Customs Enforcement, which falls under Kelly, suggest that despite the DHS chief's statement, there has been no clear change to the catch-and-release policy.

That's in large part because there are legal constraints on who can be detained and for how long, due to a shortage of beds and a court ruling limiting the stay of women and children in custody to 21 days.

“We look at each case the same way we always have," Bible said.

DHS spokeswoman Jenny Burke confirmed to Reuters that the agency has not issued new guidance for releasing migrants caught at the border.

Asked to explain why there had been no new guidance, given Kelly's statement in April, Burke said, “ICE officers make custody determinations on a case-by-case basis, prioritising detention resources.”

In a memo made public in February, Kelly defined catch and release as any policy that allows immigrants to be released from detention while they await their court hearings, making it easy to abscond. Ending catch and release was one of Trump's central promises during the 2016 presidential campaign.

Some advocates who work with migrants say they have seen little change since Trump came into office.

“Sure, people are still being released," said Kevin Appleby, senior director of international migration policy at the Center for Migration Studies. "Not because they believe in releasing them, but because there are not enough beds at the moment."

ICE declined to provide data on the number of migrants being released into the United States. But other ICE data not previously published and reviewed by Reuters shows the pool of people not in custody and awaiting court appearances is growing.

Since Trump took office in late January, the number of immigrants awaiting court proceedings while living freely in the United States has grown by nearly 30,000, rising by an average of about 7,500 per month, according to the ICE data.

During the last seven months of President Barack Obama’s presidency, the rolls of those awaiting legal proceedings outside of custody grew more rapidly, at an average of about 20,600 people per month.

Part of the slower rate under Trump can be traced to a 58 percent drop in apprehensions of people crossing the border.

Still, the numbers suggest the Trump administration is a long way from ending catch-and-release.

In part that is because his administration has come up against the reality that there simply is not enough space in detention centers.

Congress has funded about 34,000 beds to detain immigration violators, and the average daily population of detainees has been near or above capacity since before Trump took office.