In Brooks County, Texas, where the mercury regularly tops 100 degrees in the summer, Chief Deputy Benny Martinez says he prays for rain — because it keeps the body count down.
Even though his county is 70 miles north of the border, it's a crossing point for undocumented migrants coming from Central America, the source of a surge that has plunged the U.S. immigration system into crisis.
"We have recovered 37 bodies this year," Martinez told NBC Nightly News. "And it's fair to say every one we recover, we are missing five or 10. There's a lot of bodies out there."
Last year, Border Patrol documented 445 deaths of migrants coming to the United States — the third-highest number since 1998. The National Foundation for American Policy estimates an immigrant trying to sneak into the country today is eight times more likely to die than one a decade ago.
Even more troubling, the number of children — especially those traveling without their parents — is surging. Law enforcement officers say more of them are meeting tragic ends as they confront dangerous conditions on rough, shadeless terrain during their 1,000-mile journey.
"I really do pray for rain every day," Martinez said. "We need some help with moisture to keep the body count down."
This report is part of a look at the border crisis, "Desperate Journey: Children at America's Border." Check back for more on NBCNews.com and Nightly News With Brian Williams this week.
Elias Pompa, a reserve deputy, has seen an increase in women and children coming through what ranchers have dubbed "Death Valley."
"It hurts me sometimes to turn them in, but it's my job," he said.
They are turned over to federal detention centers, which have been overwhelmed by the rise in under-18 arrivals and have been scrambling to find shelter for them.
Many women and children surrender right after making it across the Rio Grande, but for those who continue on through the ranch lands of south Texas, the danger grows.
"It's harsh terrain," Pompa said. "I walk an hour and am out of breath...If you don't have a compass or guide, you're not gonna get out."
Edgar Tuaca, a 20-something Guatemalan, knows the perils well. He left his home country on June 17 and surrendered in Brooks County on July 8, clambering out of some brush near the roadside.
"Three days I was in there," he said, crying. "I couldn't hold on."
Three or four smugglers led his group across the desert. He paid about $3,000 and was told the trip would require two hours of walking. Instead, he and the others trudged endlessly in the blistering heat with no water or food.
Tuaca said he made it farther than some.
"Bit by bit people were getting left behind," he said. "If you could hang you were fine, but if not, they left you behind.
"I was there, left for dead, for three days," he added. "One leg is completely swollen, my other knee is the same, and I just couldn't walk anymore.
"Better for me to turn myself in," he said.
The transportation worker had hoped to make it to a friend's house in Virginia. Instead, he will be put into detention and potentially deported to Guatemala without the money he hoped to make to help a cancer-stricken nephew.
He said if that happens, he would not attempt the odyssey again.
"Those who do cross it it must be because they're lucky or because they have God with them," he said.