EAGLE PASS and SAN ANTONIO, TEXAS -- Along the Pan-American Highway in Colombia’s Cauca Department, Juan Guillermo Sicilia Álvarez fell unconscious the morning of Jan. 4, surrounded by other migrants traveling on the transcontinental thoroughfare.

He was the first migrant to die in the Americas this year, according to data compiled by the International Organization for Migration's . Local media he was 30 years old and from Venezuela.

2019 Among Deadliest Years for Migrants Trekking to US

Migrant fatalities happen in the Western Hemisphere from the southwestern U.S. to the Caribbean Sea to Central and South America. Boats capsize and river-crossers are swept away by currents. People get lost or abandoned in the desert without water. Disease and health emergencies strike. Cars crash. Trains crush hangers-on. Fingers pull gun triggers.

2019 Among Deadliest Years for Migrants Trekking to US

By the end of August, more than 520 migrants in the Americas died or went missing and are presumed dead, making 2019 the deadliest year for migrants in five years.

2019 Among Deadliest Years for Migrants Trekking to US

Half of the deaths in the Americas this year occurred near the U.S.-Mexico border, where bodies or skeletons are regularly found in the desert. U.S. agents patrolling the Rio Grande frequently for missing children or entire families swept under the current while trying to swim across and reach U.S. soil.

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In Eagle Pass, Texas, Border Patrol agents drive a dirt road parallel to the river all day and night, on the lookout for people who just made the crossing. Several well-worn pathways from the river, through scratchy, dense Carrizo cane lining the Rio Grande, end in a debris field of empty baby formula canisters, abandoned clothes and rusted food tins.

“The saying around here goes, ‘If it doesn't bite you, sting you or poke you, it's not native to this area,” Allen Vowell, U.S. Border Patrol’s acting deputy patrol agent in charge at Eagle Pass Station, said of the plants and animals along the border. “If you walk through there, you would find that to be true.”

In just this section of the boundary river, part of U.S. Border Patrol's Del Rio Sector, local officials report finding the corpses of 33 migrants in the 11 months from Oct. 1 to Sept. 3.

The previous fiscal year, during the same period from October 2017 to early September 2018, the agency reported 19 migrant deaths in the same area.

The numbers haven't been this high since the early 2000s, in years when border apprehensions topped 1 million, according to U.S. Customs and Border Protection .

Death tolls along the U.S.-Mexico border do not always correlate to how many people are crossing. There have been low numbers of deaths reported in some of the highest years for apprehensions, like the late 1990s, and high deaths during the lowest years of apprehensions.

But this year, with an unprecedented number of families with young children crossing into the U.S. without authorization, Border Patrol agents in Eagle Pass say they are conducting more than four times as many rescues as last year — 476 so far in the current fiscal year compared to 111 during the same period a year earlier.

“The water looks very calm and looks shallow,” explained Russell Church, interim Border Patrol agent in charge at the Eagle Pass South Station, who works with search and rescue personnel. “It changes very rapidly. It can go from just a few feet to more than 10-feet deep — and they just step off that ledge, step off that boulder, and now they're in running water.”

People by swimming, wading or rafting across — sometimes in inflatable swimming pools made for children.

In May, Eagle Pass border agents recovered the body of a 10-month-old who died when a raft carrying nine people . The odds of death on the migrant trails of North and South America vary, depending on when, where and how a traveler crosses.

In Arizona, where the border passes through rough, remote desert terrain, dehydration and heatstroke can be fatal. Every year, dozens of bodies are found — so many that a was created to track them. So far in 2019, officials recovered 111 bodies, some dead for less than a day, others that went for more than six months before being discovered.

With temperatures regularly over 42 degrees Celsius in summer along the border, “There's not enough water you can carry by yourself to carry you through for a day or two,” said Joel Martinez, deputy chief patrol agent for the Border Patrol’s Laredo Sector in Texas. “There's no way — your body's going to give out.”