It's common for groups to wait quietly before making it across.
The Border Patrol's more than 173,000 encounters with migrants on the Mexican border in April were the highest level since April 2000, though the numbers aren't directly comparable because more than six of 10 last month had been expelled. Being expelled carries no legal consequences, so many people try to cross multiple times.
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Authorities encountered 17,171 children traveling alone in April, the highest number since an all-time high of 18,960 in March.
ABC13 took a trip to the Rio Grande Valley and discovered there were a lot of "eyes" all along the border.
"You know what, I would never believe that if I wouldn't see for my own eyes," said Raul Cruz, who lives in the Rio Grande Valley.
Cruz has been recording videos of crossings himself for several months.
"Some say it's a crisis, some say it's not. Let everybody decide on their own," he said.
Cruz took ABC13 anchor Mayra Moreno on a private boat ride along the river to show her just how it's happening. All along the windy river were signs of life, including deflated rafts, plastic water bottles and sometimes clothes.
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"There in the Mexico side, you see some kids ... it appears they are fishing," said Cruz during the tour.
But more often than not, Cruz said they can be scouts pretending to fish and passing along information.
"If you notice when we got here, two of them went up to the top of the hill," explained Cruz.
Eyewitness News eventually came across a group of men from Guatemala. They said they were getting ready to cross, but said the immigration patrol boats were coming. Within seconds, Border Patrol agents on boats came racing through.
The question is, how did they know? ABC13 spotted a man a few hours earlier near the docking area. He appeared to be "hanging around." Cruz believes that man may have been the group's informant.
There were about 50,000 people encountered in families in April. About one of every three families was expelled to Mexico. The rest were allowed to remain in the United States to seek asylum.
The Associated Press contributed to this report.
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