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. No homes appeared immediately threatened by the flow.

Ponton said a levee broke across the Rio Grande in neighboring Ojinaga, Mexico, where Presidio Mayor Lorenzo Hernandez said homes and other buildings have been inundated with up to 10 feet of water.

"Things are pretty rough right now, but I guess they could be worse," Hernandez said Tuesday night. "The water is up to the roofs in Mexico."

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-stricken Luis Leon Reservoir in Mexico pushed the Rio Grande over its banks, filling wide channels between the earthen levees on either side of the border.

By late Wednesday morning the river level had dropped slightly and Presidio officials were being told that water releases from the Luis Leon had been slowed, Ponton said.

"Hopefully we can continue to see moderate decreases of the Luis Leon releases and flows in Presidio," 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," Ponton said. "The water pressure could find a weakness."

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 prompted officials in Presidio to go door-to-door Tuesday 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 connecting Presidio to Ojinaga.

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 in low-lying areas 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.

Since the heavy rains, Mexican officials have been forced to release water from the Luis Leon Reservoir into the Rio Conchos, which flows into the Rio Grande not far from Presidio.

The U.S. and Mexican leaders of the International Boundary and Water Commission were on their way to survey the situation Monday when their plane disappeared. The search continued Wednesday for U.S. commissioner Carlos Marin and his Mexican counterpart, Arturo Herrera. Jake Brisbin Jr., executive director of the Rio Grande Council of Governments, also was on board.