The young girl is in her father's shirt, his right arm around his neck as they lie near the shore. They were discovered on the Mexican side of the Rio Grande.
The government of El Salvador identified her as Oscar Alberto Martinez and his daughter Angie Valeria M.
The child was 2 years old, reported The Associated Press.
In the photo, the corpses have come to rest near a river bank, where five discarded beer cans and an empty soda bottle sit in the high reeds. Another beer can swims next to the girl's body.
Salvadoran officials said the father and daughter drowned on Sunday. Her bodies were found on Monday.
Salvadoran Foreign Minister Alexandra Hill said the government is working with the Mexican authorities to repatriate the remains.
"Our county mourns again, I beg you, all families, parents, do not risk it," she said, according to a CNN translation. "Life is worth more."
This is an evolving story. Return for updates.
Andrea Diaz of CNN contributed to this report.