NUEVO LAREDO – About 18 000 people were evacuated today from a town in northern Mexico where authorities fear a dam will overflow in the wake of Hurricane Alex.Evacuees were taken to shelters in nearby towns and cities, Ciudad Anahuac Mayor Santos Garza Garcia said.Garza said 12 floodgates have been opened but authorities had not been able to open 17 others because of electrical failures. He said the dam, is releasing 600 cubic meters per second into the Salado River, a tributary of the Rio Grande, and could overflow soon.“The situation is very critical,” Garza said at a news conference. (AP)