PRESIDIO, Texas — The swelling Rio Grande flowed over a levee Wednesday, sending water cascading onto the golf course and some ranch land in this dusty-turned-muddy West Texas border town.

The levee had not failed, said Presidio County Attorney Rod Ponton, but an area on the eastern end of Presidio was turned into a chocolate-brown reservoir marked by partially submerged trees, bushes and power lines. By Wednesday afternoon, the water had crept into the backyards of several homes on a small bluff between the golf course and the city of Presidio, but no homes appeared under threat.

A levee broke across the Rio Grande in neighboring Ojinaga, Mexico, where Presidio Mayor Lorenzo Hernandez said homes and other buildings received up to 10 feet of water.

Muddy water covered roads and structures within eyesight of the shuttered border crossing in Ojinaga. Two large chunks of earth were ripped from the narrow levee that once held back the river. Mexican officials in boats were seen Wednesday patrolling the flooded area that extended at least a half mile from the border crossing.

Flood waters had risen to rooftops of homes and other buildings in some spots on the Mexican side of the Rio Grande.

Officials in Presidio, a town of 5,000 people about 250 miles down river from El Paso, have been watching the Rio Grande for nearly two weeks. Heavy rains and water releases from the flood-swollen Luis Leon Reservoir in Mexico pushed the Rio Grande over its banks, filling wide channels between the earthen levees on both sides of the border.

By late Wednesday morning, the river level had dropped slightly, though the swirling water appeared to be just below the top of the levee at the international bridge connecting Presidio to Ojinaga. Presidio officials were also told that water releases from the Luis Leon had been slowed, Ponton said.

Ponton said the city could remain threatened for several days after record water levels filled the wide channels between earthen levees on both sides of the border.

"These levees are not designed to be dams," he said. "The water pressure could find a weakness."

"When they built these new levees this wasn't supposed to happen," said Tammy Bishop, whose family owns the golf course and a nearby farm.

"It's 18 holes. Or was," Bishop said of the golf course-turned-lake. "It's 10 feet deep."

Low-lying parts of Presidio are under mandatory evacuation, but schools remain open even as the elementary school serves as a temporary shelter for about 80 displaced residents.

Ponton said if the levee does break, low-lying parts of the city, including hundreds of homes, would be gradually swamped.

"If it does go it could be the same effect as in Ojinaga," Ponton said. "But we're just talking about water gradually rising up ... making homes uninhabitable and roads impassable. It would rise slow enough that people would be able to leave."

The flood threat had prompted officials in Presidio to go door-to-door urging people to leave. They made the same plea from a helicopter. U.S. Customs and Border Protection officials also shut down the international bridge.

Earlier this week, officials said the evacuation affected about 500 people in the Presidio area.

Presidio Police Chief Marco Baeza said a few older residents living in low-lying areas have opted to stay.

"One said, 'I've been here 58 years and nothing's happened before and nothing's going to happen now,"' Baeza said.

The recent rains and flooding aren't related to Hurricane Ike, which hit hundreds of miles to the east.

The U.S. Border Patrol said Wednesday that it had located a plane that had been carrying the U.S. and Mexican heads of the International Boundary and Water Commission sent to survey the situation. It had disappeared Monday with four people on board.

The agency, which maintains the border levees on the Rio Grande that separates the two countries, confirmed the deaths of U.S. commissioner Carlos Marin and his Mexican counterpart, Arturo Herrera. Jake Brisbin Jr., executive director of the Rio Grande Council of Governments, and pilot Matthew Peter Juneau were also killed.

The Border Patrol said it found the plane's wreckage in a rugged section of the Sierra Madre Mountains in Mexico, about 20 miles northwest of Presidio.