McALLEN, Texas – Under a quarter moon, just past midnight, a call blared from the Border Patrol radio that a law enforcement helicopter with infra-red sensors had spotted a group of illegal immigrants crossing the Rio Grande into the United States.

In response, Border Patrol agents raced along rough dirt roads to reach the area. In the beam of the helicopter searchlight they found the immigrants running through newly irrigated sorghum fields. The furrows between the crops were slippery with mud, which hampered the agents’ pursuit. 

Mark Potter/NBC News
Patrol supervisors Rick Moreno and Jose Trevino patrol near the Rio Grande in Texas at sundown. 

Of the 20 people spotted by the helicopter team, ten were eventually rounded up. The rest either swam back to Mexico or hunkered down in the field to escape detection.  Those who were caught were transported to a Border Patrol office for identification, processing and a determination of whether they would be prosecuted or returned to their home countries.

For the agents in the muddy field, it was just another night on patrol along the Rio Grande in south Texas, where the flood of illegal immigrants never stops.

Illegal immigration on the rise here In the Border Patrol’s Rio Grande Valley sector, which stretches from Brownsville west past McAllen to Rio Grande City, agents are starting to see a slight increase in the apprehensions of illegal immigrants when compared to last year.

Along the entire length of the Southwest border, from Texas to California, illegal immigration seemed to have taken a nosedive in recent years, with apprehensions in fiscal year 2009 falling to 540,865 compared to 705,005 in fiscal 2008.

Many believe the drop was the result of fewer jobs being available for immigrants in the U.S. after the economic downturn. Others credit increased law enforcement efforts and high-tech detection methods with deterring illegal crossings. On Tuesday, President Barack Obama ordered 1,200 National Guard troops to the border to boost security.

In the Rio Grande area, though, immigration arrests have risen 4 percent this year and most notable is the increase in what agents call OTMs – Other Than Mexicans – immigrants from 74 different countries who have been picked up here. They represent nearly a third of all illegal immigrants detained in the sector and come mostly from Central America, but also from as far away as China and the Middle East.

"One of the reason OTM's are drawn to this particular area is that we're the closest tip to Mexico," said J.R. Villarreall, the Assistant Chief of the Border Patrol's Rio Grande sector.  "Many of them migrate through Mexico and we're the closest place where they can enter the United States."

Mark Potter/NBC News
Border Patrol agents Henry Davis and Arturo Vela patrol the Rio Grande by boat.

Riding the river In Texas, the dividing line between the United States and Mexico is the middle of the Rio Grande, which in the McAllen area runs wide and fast with treacherous currents. 

Patrolling the river on a Border Patrol boat with powerful but quiet four-stroke engines, agents Henry Davis and Arturo Vega kept a close eye on the Mexican shoreline. They were watching for signs that groups of immigrants might be getting ready to illegally cross the river. Small cuts in the brush on the Mexican side revealed where immigrants would enter the water. Hundreds of worn spot on the American side are where the undocumented travelers came ashore. They are a little bit downriver from the Mexican launch sites – to account for the current flow.

"It’s constant, constant. This is one of the hottest spots we have right here, in this zone," said Davis. "It's non-stop every day, 24 hours a day," agreed Vela.

The safest way for immigrants to cross the river is in rafts provided by smugglers. But some of them use other, less secure methods to stay afloat.

"We’ve seen them use everything from a raft to a water jug, two-liter soda bottles that they’ll cap and tie a string to and throw under their arms," said Jose Trevino, a Border Patrol supervisor. "Trash bags have even been used.  They fill them with air and tie them off."

Some of the immigrants drown in the river, leaving U.S. Border Patrol agents to retrieve the bodies and return them to Mexican authorities.

During a recent flight along the border, a helicopter pilot watched a swimmer in the river who seemed to be struggling.  By radio the pilot alerted U.S. agents in the area to the man's plight, but eventually the swimmer turned around and made it safely back to the Mexican side. Not all are that fortunate.

Mark Potter/NBC News
Moreno and Trevino search a thicket along the Rio Grande near McAllen, Texas.

Just north of the Rio Grande, on the U.S. side of the border, the immigrants and their guides have carved a widespread network of trails in the thick underbrush. Agents said whenever they discover and shut down one trail, another seems to pop up quickly.

"There’s hundreds of thousands of them. Just in this half-mile radius, you’ll probably see a hundred," said Border Patrol supervisor Rick Moreno. "As people come walking through they start developing a trail. And to avoid getting lost, aliens, undocumented workers, will keep to that trail."

The terrain around the river is hilly in spots and is often covered with thick vegetation where the immigrants can hide from U.S. agents. "This area is hard to patrol," said Border Patrol supervisor Jose Trevino, pointing toward the high grass along a trail.  "There's a lot of brush, a lot of underbrush and a lot of trees. When you combine both of them, there's a lot of hiding points."

Farther up the road in the border cities, smugglers will often hide the illegal immigrants in safe houses until arrangements can be made to transport them to other areas. Authorities found one such house recently in Alamo, Texas, with 67 people crammed inside, sharing bedding, food and limited bathroom facilities. The one-story house was on a major road, across the street from a high school.

Running into drug traffickers In addition to intercepting immigrants, Border Patrol agents must also be alert to the dangers of encountering drug traffickers smuggling tons of marijuana, cocaine, heroin and methamphetamine into the United States along the riverbank.  They often float the drugs  – primarily marijuana – across the Rio Grande in rafts and inner tubes before bringing it ashore on the American side.

During a recent night operation, Border Patrol agents searched for drug smugglers in a field covered with tall grass and bushes. They located and arrested one of the suspected smugglers and found ten bales of marijuana hidden in the brush for pick-up. They also took note of several people passing by in cars. The agents believed they were spotters hired by the traffickers to keep an eye on U.S. law enforcement officials. "They watch us every day, every day.  Their counter surveillance is pretty intense," said Trevino. 

The next afternoon, agents hiding in the grass spotted another group of people starting to smuggle a marijuana load across the river, but a helicopter passing by startled the smugglers and they turned back.  A short time later, on a muddy road along the American side of the river, agents found two cars with their back seats removed, most likely to make room for the marijuana bales which were supposed to have arrived from Mexico.

While the number of illegal immigrants apprehended dropped along the border in recent years, law enforcement officials say marijuana seizures have skyrocketed upward.

A 24-hour threat along the border The U.S. Border Patrol mans the river area 24 hours a day, using three overlapping shifts.  Unlike other areas of the border – including Tucson, El Paso and Brownville – which have stationary camera system to assist the agents, there is no such system in the McAllen area, despite its heavy load of illegal immigrants and drug smugglers. Agents say it would be very helpful to have monitored camera back-up providing extra eyes in the sky.

As it stands now, agents in this sector rely on heavy manpower, electronic ground sensors, portable night scopes, helicopter surveillance and their own close-working knowledge of the area and the threats there.

"The agents are faced with a difficult situation every day," said Villarreal. "They know they are coming out there to protect the border.  They don't know what they're going to encounter that particular day.

 Source : http://fieldnotes.msnbc.msn.com/archive/2010/05/26/2329012.aspx