A plane carrying the U.S. and Mexican heads of the International Water and Boundary Commission disappeared Monday while touring floods along the Rio Grande.

Commissioners Carlos Marin, of the U.S. section, and Arturo Herrera, from Mexico, were flying to Presidio, Texas, from El Paso but the plane did not land as scheduled, Presidio County Judge Jerry Agen said. The plane carried the pilot and one other passenger, he said.

The chartered Cessna 421 propeller plane left about 10 a.m. and was to fly over a reservoir in Mexico so the men could see a dam where water is being released to ease flooding, said Sally Spener, a spokeswoman for the IBWC in El Paso.

Agen said searchers were looking in a rough, mountainous section of desert about 60 miles west of Presidio. "It's a rough area out there, with very few roads," Agen said.

Spener said the Federal Aviation Administration, the U.S. Air Force and the U.S. Border Patrol were involved in the search, though she could not confirm the search area.

Marin and Herrera head the international agency responsible for maintaining the border between the U.S. and Mexico. Each man's office inspects and maintains river levees along the Rio Grande.

In the river town of Presidio, the swollen Rio Grande has crawled up its levees, and both countries have evacuated residents in low-lying areas near the river.

Authorities fear that if the earthen levees fail, water would pour into Presidio and the Mexican town of Ojinaga.