Border Patrol agents park along the banks of the Rio Grande in Eagle Pass, Tex., in early April. (Sergio Flores for The Washington Post)

U.S. border agents along the Rio Grande recovered the body of a 10-month-old boy Thursday and continued searching for two other children and a man who remained missing after their raft capsized while crossing the river near Eagle Pass, Tex., according to U.S. Customs and Border Protection.

The missing include a 7-year-old boy and a girl approximately the same age, part of a group of nine Honduran migrants who were attempting to cross the river late Wednesday, said Department of Homeland Security officials who described the incident on the condition of anonymity to disclose information not yet publicly released.

Drownings and migrant rescues along the Rio Grande are a regular occurrence, but the dangers have increased in recent weeks, with the river swollen with spring runoff at a moment when record numbers of Central American families are attempting to cross — typically in flimsy dinghies with no safety gear.

Unauthorized border crossings surpassed 103,000 in March, the highest level in a dozen years, and a majority of those arriving are part of family groups. The powerful currents of the Rio Grande have long been a deadly risk to migrants, but they pose an especially grave danger now because so many small children are making the journey to the U.S. border with their parents.

“What we’re dealing with now is senseless tragedy,” Raul L. Ortiz, the top Border Patrol official in the Del Rio, Tex., sector, said in a statement, blaming “callous smugglers” who “imperil the lives of migrants for financial gain.”

The experimental U.S. policy requires migrants to wait in Mexico while their asylum claims are processed. Homeland Security officials said the measure will soon expand to multiple border cities and apply to migrant families. (Luis Velarde /The Washington Post)

According to CBP, U.S. agents encountered a man late Wednesday who said his wife and two sons — a 10-month-old and a 6-year-old — had fallen into the river, along with his nephew, age 7. Another man and a female child were also reported missing.

“Shortly afterward, cries coming from the river alerted agents to the riverbank where two people, a woman and a child, were in distress, struggling to stay afloat,” the CBP report states.

A Border Patrol agent jumped into the river and rescued the woman and child, who were later identified as the wife and son of the man who made the initial report, according to the agency. The 6-year-old boy was taken to a hospital for advanced treatment.

CBP agents found a man and a boy a short time later on the U.S. side of the river.

Border Patrol rescue teams began searching for the three still missing, and the body of the 10-month-old was found several miles downriver Thursday morning, CBP said.

Last year, border agents and CBP rescue teams responded to 4,300 emergencies along the U.S.-Mexico border, according to the agency. CBP recorded 283 deaths in fiscal 2018, down from a peak of 492 in 2005 — a statistic that includes drownings along the river, accidents and the discovery of human remains in desert areas.

On Tuesday, a 16-year-old from Guatemala died in Texas 10 days after crossing the border. Guatemalan officials said the teen fell sick shortly after his arrival and was taken from a U.S. shelter for unaccompanied minors to a Texas hospital. The officials said the teenager had a brain infection and died while receiving treatment.