On the Suchiate River dividing Mexico and Guatemala, it sure looks easy to cross north without papers.

A young, mustachioed man is pulling a makeshift raft across the quiet river via two ropes connecting the countries. The crossing costs 4 quetzales, 10 pesos or 50 U.S. cents. The raft captain says that nearby migration officials rarely intervene.

But the impression that Mexico is lax on migrants disappears as you head just a little north.

"They put up lots of checkpoints," says Gustavo Rivera, a bus driver shuttling between Mexico's southeastern border and the nearest city, Tapachula. "Immigration [agents], federal police, soldiers, local police. I don't get many migrants on the bus anymore because of the checkpoints."

President Trump singled out a group of families from Guatemala, Honduras and El Salvador heading to the United States as evidence that "Mexico is doing very little, if not nothing," to stop immigration. But Mexico has actually assembled an aggressive enforcement strategy, with U.S. backing.

The strategy tightened up in 2014, shortly after American officials declared a crisis over the arrival of large numbers of Central American children at the U.S. border. The U.S. began funding Mexico's immigration crackdown with the Southern Border Plan.

Rather than amassing troops on its border with Guatemala, Mexico stations migration agents, local and federal police, soldiers and marines to create a kind of containment zone in Chiapas state. With roving checkpoints and raids, Mexican migration agents have formed a formidable deportation force. Since the Southern Border Plan launched, Mexico has deported more than half a million Central Americans, including almost 82,000 last year, according to data from Mexico's Interior Department. Since 2015, Mexico has deported more Central Americans annually than U.S. authorities have, in some years more than twice as many.

It's such an effective force that even some government officials try to give migrants workarounds.

"We often tell migrants to travel at night," says Ana Carolina Rodas, who runs the state government's local migration assistance office in Ciudad Hidalgo, the small town that abuts the Guatemala border. "There are fewer migration officials or checkpoints at night, so it's less likely they'll be detained and deported."

In recent years, nearly half of migrants detained in Mexico haven't made it past southernmost Chiapas state.

"We feel safe here"

On a baking Tuesday afternoon in Tapachula, the largest city on Mexico's southern border, dozens of Hondurans, Guatemalans, Salvadorans and Nicaraguans crowd into the shade of trees outside the Belén shelter. Its front yard has become the main hangout for migrants in the city.

"Everyone, especially women and children, hangs out here all day," says Ricky, an asylum-seeker from El Salvador. All the people outside the shelter asked NPR to only publish their first names for fear of being located by gangs and authorities after fleeing violence or threats in their home country. "We feel safe here because if anything were to happen, we'd all support each other."

Migrants used to roam all over Tapachula. They'd rest under the central park's pavilion during the day, enjoying the free entertainment of street performers. They'd pack an adjacent street where restaurants cater to the tastes of Salvadorans, Hondurans and Cubans. At night, migrants who couldn't afford or find a bed tucked themselves away under the park's concrete benches. No more.

"I've been sleeping here on the sidewalk outside the shelter for almost a month," says Ricky, who used up the limit that the shelter would allow him to stay there. "But it's better than wandering through the city, where you'll get picked up and deported."

"We have become a target"

Beti rests against a tree with her 4-year-old son. The two left Honduras in March and are requesting asylum in Mexico. They don't feel particularly welcome.