The farmers armed themselves with sticks, rocks and homemade shields, ambushed hundreds of soldiers guarding a dam and seized control of one of the border region’s most important bodies of water.

The Mexican government was sending water — their water — to Texas, leaving them next to nothing for their thirsty crops, the farmers said. So they took over the dam and have refused to allow any of the water to flow to the United States for more than a month.

“This is a war,” said Victor Velderrain, a grower who helped lead the takeover, “to survive, to continue working, to feed my family.”