The victim’s nationality or cause of death are not known.
Mexico’s foreign ministry said in a statement that it was “concerned about the impact on the human rights and personal security of migrants that this border policy has.”
The 300-meter-long barrier, made up of scores of large orange buoys, was erected in July at a crossing point of the Rio Grande that many migrants use. In addition, barbed wire has been erected on the beach on the American side.
The barriers were put in place by order of Texas Governor Greg Abbott.
In response, the US Department of Justice has sued Texas, arguing that the barrier lacks a permit and also impedes traffic in the river.
Mexican President Andrés Manuel López Obrador has said the barriers violate his country’s sovereignty.
Hundreds of migrants die each year along the US-Mexico border, often trying to cross the Rio Grande.