An alleged plot by a Mexican drug cartel to blow up a dam along the Texas border — and unleash billions of gallons of water into a region with millions of residents — sent American police, federal agents and local disaster officials scrambling last month to thwart such an attack, authorities confirmed Wednesday. Whether the cartel, which is known to have stolen bulk quantities of gunpowder and dynamite, could have taken down the five-mile-long Falcon Dam along the Rio Grande River may never be known. But it may have been derailed by a stepped-up presence by the Mexican military, acting in part on intelligence from the U.S. government, sources said. The warning was based on what the federal government contends were “serious and reliable sources” and prompted the Homeland Security Department to sound the alarm to first responders all along the South Texas-Mexico border. Mexico’s Zeta cartel was planning to destroy the dam not to terrorize civilians, but to get back at its rival and former ally, the Gulf cartel, which controls smuggling routes from the reservoir to the Gulf of Mexico, the Zapata County sheriff and others familiar with the alleged plot said. Destroying the dam, however, also would have flooded large areas of agricultural land, as well as significant parts of a region with about 4 million border residents in Texas and Mexico. Besides the sheriff’s agency, the U.S. Border Patrol, the Texas Department of Public Safety (DPS), and even game wardens, also responded. Citing security concerns, neither Homeland Security nor DPS commented.

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