For five generations, the Benavidez family has lived on a seven-acre plot of serene farmland near the U.S.-Mexico border west of Brownsville, Texas. They've harvested cotton and squash and raised goats and pigs. They've helped sculpt the levee that snakes across the rear of the property. They've given birth there, married there and died there. Their connection to the land runs so deep that they can't imagine parting with even a piece of it. So two weeks ago, when federal employees arrived asking to purchase a rectangular slice abutting the levee for $4,100 to make way for a border fence aimed at deterring illegal immigrants, they refused. "I don't want to scare you," Idalia Benavidez, 77, says one of the employees told her, "but whether you agree or not, the government's going to make the fence." If the Feds get their way, an 18-foot-high barrier will soon traverse the Benavidez property, cutting off their cows from a pasture south of the fence's proposed path. "It's going to be ugly," says Benavidez. Worse still, she predicts, "it's not going to work."

That mostly sums up the current sentiment along the Texas border. But the Brownsville area in particular—where a unique alliance of politicians, business leaders, farmers, environmental activists, church groups and ordinary citizens has challenged the fence—has become the epicenter of the fight. On April 28 many of those constituencies plan to air their grievances at a congressional field hearing in the city designed to examine the fence's impact. Opponents decry "the wall," as they call it, as a waste of money better spent on more border personnel and surveillance technology. They lament what they consider outsiders' misunderstanding of south Texas culture, with its Anglo-Mexican blend and its view of the Rio Grande as a meeting point rather than a dividing line. And they argue that it will crimp the economy and trample landowners' rights.

Chief among their concerns is the possibility that the fence will despoil the environment. In early April, wielding authority Congress granted him in 2005, Department of Homeland Security Secretary Michael Chertoff waived three dozen laws that he said interfered with his ability to build the fence. Among them: the Endangered Species Act, the Clean Air Act and the Safe Drinking Water Act. Environmental groups have challenged three previous waivers, but have lost each time. Now the groups are petitioning the Supreme Court to review one of those decisions.

The fence's proposed path would slice through parts of the Lower Rio Grande Valley National Wildlife Refuge—90,000 acres of prized nature preserve that the U.S. Fish and Wildlife Service has been slowly buying up and restoring over the last 30 years. The refuge contains 17 endangered or threatened species, including two cats: the ocelot and the jaguarundi. It's home to 500 species of birds, 300 species of butterflies and 1,200 species of plants. And it's the only place in America where some of those birds—like the red-billed pigeon and the brown jay—can be seen. Wildlife experts fear that the fence would block river access for animals and disrupt their habitat.

Any environmental damage could have pocketbook consequences as well. Nature enthusiasts help fuel a $125 million-per-year ecotourism economy in south Texas. But some of the places that draw them may soon be walled off. For instance, a Nature Conservancy preserve east of Brownsville that's populated by stands of sabal palms and rare birds like chachalacas would wind up on the Mexican side of the fence. "We're considering the possibility of giving up this area," says project manager Sonia Najera. Up the river in Alamo, Keith Hackland, who owns a bed and breakfast that caters to bird lovers from all across the world, worries that his clientele may head elsewhere. "They might not want to go when bulldozers are ripping down the remnants of our birding forests," he says. "To a birder, that's just agony."

Worries like these have prompted clashes among government officials. Ken Merritt, a Fish and Wildlife manager who used to oversee the National Wildlife Refuge, says he struggled to get information from the Department of Homeland Security about the fence. "One week, the fence would be one place; the next, it would be somewhere else," he says. "It was just chaos … I don't think DHS is sympathetic to the wildlife corridor." But his biggest headaches came from his own agency. When he failed to approve an engineering survey for the fence, deeming it too disruptive, Fish and Wildlife's Southwest regional director, Benjamin Tuggle, "really applied the pressure for me to" approve it, says Merritt. "He made it very clear that he thought I was making decisions that were career ending." After 30 years of service, Merritt quit in January. Tuggle had his own complaints about the fence; in March, he lobbied his superiors to inform DHS that the fence wasn't "compatible" with Fish and Wildlife's mission. He says he only wanted Merritt, who had approved two other wall-related studies, to be consistent. "I can tell you unequivocally that at no time did I ever make any inference to threaten Ken Merritt's career," he says.