The agency's Tactical Marine Unit (TMU) found the bodies over a 48-hour span.
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On Saturday, July 1, U.S. Border Patrol called for help regarding an infant who appeared to have drowned, according to Lt. Chris Olivarez.
Olivarez said TMU deployed two airboats and saw multiple bodies floating along the river. Four people were recovered and placed on the boat.
A woman and the baby girl were unresponsive. Authorities performed chest compressions, but both had to be transported to Fort Duncan Regional Medical Center where they were pronounced dead.
The two survivors pulled from the water were turned over to USBP, Olivarez said.
The next day, on Sunday, July 2, a male was pulled from the river. Then, on Monday, a female's body was recovered from the water in a separate incident.
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Olivarez said the identities are unknown as none of them were carrying identification.
The deadly discoveries come just days before Texas deploys new border buoys, or floating water barriers, on the river to prevent migrant crossings in heavily trafficked areas of the Rio Grande Valley.
Governor Greg Abbott plans to launch the first 1,000 feet of barrier near Eagle Pass, which shares the border with the Mexican city of Piedras Negras, on Friday.
The buoys will range in size, but will be about four feet long, officials said.
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Still, immigrant advocates say the barrier will only increase the likelihood people will drown attempting to cross.
In addition, the current near Eagle Pass can be particularly dangerous. There are areas that are sometimes shallow enough to cross on foot, but sudden, steep drop-offs and a strong current has led to drownings.
This is also the area where a Texas National Guardsman drowned while attempting to save migrants who appeared to be in distress in April 2022.
ABC News contributed to this report.