New Delhi, Oct. 14 -- Fifteen minutes before water from a flooded stream swept into her home, Lilia Ramirez took off running with what little she could carry. When she returned she found not only damage from the water that had flooded her first floor to the ceiling, but the oil it had carried now streaking her walls.

Poza Rica is an oil town, and among the challenges confronting some residents who fled flooding that has killed 64 people across five states and left 65 missing, is residue from the oil that built this city not far from the Gulf of Mexico. Authorities say some 100,000 homes across the region have been damaged by the torrential rains and flooding.

"Never before has it been tarred before like that," Ramirez said Monday standi...