| REYNOSA, Mexico
REYNOSA, Mexico Tougher security along the U.S.-Mexico border is forcing migrants to take more dangerous, remote routes to cross into the United States and pushing up the number of deaths in the desert.
This year could see a record of well over 500 such deaths. At least 275 Mexican bodies have been found in the first six months, according to a Mexican Congressional report backed by U.S. and Mexican border groups and academics.
They say at least 4,500 Mexicans have died trying to cross since the United States drastically increased border controls in late 1994 to stem illegal immigration.
Following the failure of President George W. Bush's immigration reform proposals in Congress last month, U.S. policy is centered on tighter border security rather than giving immigrants more options to find jobs legally.
But some border experts say enforcement does not stop those trying to get into the United States and only makes it more dangerous, greatly raising the fees charged by people smugglers. As security increases, so will the number of deaths, they say.
"Has enhanced border security increased the number of migrant deaths? Unquestionably," said Wayne Cornelius, an immigration expert at the University of California San Diego. "There is no other way to explain the sharp increase in fatalities."
The Border Patrol recovered some 116 bodies in the Arizona desert between last October 1 and the end of June, and it only records deaths on the U.S. side of the frontier. It blames ruthless smugglers for taking migrants through dangerous terrain and sometimes abandoning them there.
"The number of migrant deaths is increasing because smugglers are taking them to less-patrolled, more dangerous areas," Border Patrol spokesman Ramon Rivera said. He said agents rescued 1,450 people in the desert in the same period.
Unknown numbers of migrants from Central America and other countries also die each year.
The U.S. government has raised its Border Patrol deployment to around 13,500 agents today from fewer than 4,000 in 1993 and plans to add a further 9,600 agents by 2012. It deployed 6,000 National Guard troops to the border last year for a two-year period until more agents are hired.
Washington aims to have "operational control" of the border by 2013 by building a 700-mile (1,120-km) wall along parts of the frontier and creating a "virtual fence" in desert areas with drones, sensors, cameras, satellite technology and vehicle barriers.
Before the stepped-up enforcement operations, experts say most deaths were due to traffic accidents as migrants dashed across freeways in border areas. Today, most die from hypothermia in the desert or by drowning in the Rio Grande and irrigation canals.
Many Mexicans seeking work in the United States try the overnight trek through the hostile Arizona desert and away from urban areas such as Tijuana on the California border.
Between 2000 and 2005, 802 bodies were found in the desert, compared to 125 between 1990 and 1999, according to the University of Arizona.
Surveillance is expected to increase in the Arizona desert but some experts say that will simply encourage more people to try to cross remote swamp areas of the Rio Grande in Texas.
"As they increase enforcement in Arizona, we will see a shift toward the eastern and western fringes of the border. In Texas, we are already seeing more drownings," said Claudia Smith of the California Rural Legal Assistance Foundation, which campaigns for immigrants' rights.
Migrant shelters in Mexican border towns say they see no sign of less illegal immigration despite a fall in Border Patrol arrests. Some shelters, such as in Reynosa in northeastern Mexico, are expanding to offer more beds.
U.S. wage levels that are much higher than in Mexico remains the main incentive for attempting the difficult border crossing.
"I've got an uncle in Florida and the chance of something is so much better than here," said Adan Zendejas, a 24-year-old who cannot swim, as he readied to cross the Rio Grande from Reynosa on a car tire.