MEXICO CITY (Reuters) - A floating barrier of orange buoys put in the Rio Grande by the Texan government to hinder migrants crossing into the U.S. violates a water treaty and may encroach on Mexican territory, incoming Mexican Foreign Minister Alicia Barcena said on Friday.

"We have sent a diplomatic letter (to the U.S.) on 26 June because in reality what it is violating is the water treaty of 1944," Barcena told reporters in Mexico City, referring to the Mexican Water Treaty between the U.S. and Mexico that covers the use of water from the Colorado, Tijuana and Rio Grande rivers.

"We are sending a mission, a territorial inspection," Barcena added, "to see where the buoys are located... to carry out this topographical survey to verify that they do not cross into Mexican territory."

The U.S. State Department and the office of Texas Governor Greg Abbott did not immediately respond to requests for comment.

Barcena was named foreign minister last month but is still awaiting formal confirmation by Mexico's Senate.

On Friday, the Texan government said in a statement that it had this week begun installing the "new floating marine barriers along the Rio Grande River in Eagle Pass."

It said the buoys will "help deter illegal immigrants attempting to make the dangerous river crossing into Texas."

Many migrants have drowned trying to cross the river in recent years but some experts fear the buoys may only increase the risk of crossing.

Earlier this month, four migrants drowned in the Rio Grande. Last September nine migrants died and 37 were rescued as they tried to cross the rain-swollen river near Eagle Pass.

(Reporting by Stephen Eisenhammer; Editing by Sandra Maler)