Flooded houses are seen in deserted Ciudad Anahuac in the northeastern state of Nuevo Leon, Mexico after 18,000 people were evacuated from the village.

NUEVO LAREDO, Mexico (AP) – Reservoirs along the Texas-Mexico border rose to their highest levels in decades after days of drenching rain, forcing officials to close two border bridges Wednesday, dump water into flooded rivers and evacuate tens of thousands from homes as a new storm headed toward the region.

The dramatic rise of the Rio Grande caused by Hurricane Alex and continuing rains forced the closure of one major border crossing between downtown Laredo, Texas, and Nuevo Laredo, Mexico, and another crossing known as the Colombia Bridge, about 32 kilometers upriver.

Officials evacuated the flood-threatened Vega Verde subdivision in Del Rio, Texas, some 180 kilometers upstream from Laredo, while high waters in the northern Mexican state of Coahuila have already damaged some 10,000 homes — many swamped in waist-deep water.

“That means there are 40,000 people who don’t have any place to sleep,” Gov. Humberto Moreira told the Televisa network Wednesday.

To the southeast, Mexican officials evacuated nearly 18,000 people from houses in Ciudad Anahuac for fear that water would overflow the Venustiano Carranza dam and threaten lives. Mexico’s National Water Commission said the dam currently had the largest emergency water release in the country.

Ciudad Anahuac Mayor Santos Garza Garcia said at least 1,500 homes had been flooded in the town of Rodriguez, across the Salado River from his city.

Officials in Laredo urged residents of low-lying areas to evacuate.

An airplane on an inspection tour of the flood zone crashed Wednesday, killing the mayor of the border town of Piedras Negras, the state public works director, a municipal civil defense official, a government photographer and the pilot and co-pilot. The plane was flying over a rain-swollen reservoir about 40 kilometers east of Eagle Pass, Texas, when it went down.

Hurricane Alex dumped heavy rains on the region last week, causing flooding that killed at least 12 people in the Mexican state of Nuevo Leon, where Ciudad Anahuac is located, and leaving some 130,000 without water service.

The US National Weather Service said the second tropical depression of the Atlantic hurricane season had formed over the western Gulf of Mexic and issued a tropical storm watch for the Mexico and Texas coasts on both sides of the Rio Grande.

The depression was about 425 kilometers east-southeast of Brownsville, Texas. Maximum sustained winds were about 55 kph. Forecasters said it could become a tropical storm before hitting land and dumping more rain.

Water behind the binational Amistad Dam on the Rio Grande already is at its highest level since 1974, according to the International Boundary and Water Commission, forcing officials to release water from it at the fastest rate in a quarter century.

The commission said the downstream Falcon dam would probably reach capacity within the next few days, suggesting future releases there will raise water levels along the river’s lower reaches.