The lower Rio Grande forms the border between Texas and Mexico. Although it’s the fourth-longest river in the U.S. and feeds wildly diverse ecosystems along its 2000-mile course, the Rio Grande is treated like an irrigation ditch and what writer Nick Paumgarten calls a “moat” dividing the two nations. Trump’s proposed border wall would follow a large portion of it, devastating its fragile ecology without slowing the trafficking of hard drugs.

For The New Yorker, Paumgarten floated the rugged river canyons through Big Bend National Park. Camping on both sides of the border, his flotilla included such esteemed companions as Democratic Senator Tom Udall, from an influential conservation-minded family, and Teddy Roosevelt’s great-grandson.You have to see certain places to understand why they must be protected. Paumgarten’s story lets readers experience this landscape themselves, to appreciate what Trump’s wall would destroy: not only the landscape, but the opportunity to experience tranquility around campfires, for wildlife encounters, starlit nights and spiritual experiences, and the chance for future generations to connect with nature.

Having been determined by the 1848 peace treaty that ended the Mexican-American War, the border traces the river’s deepest channel—the thalweg—which, because the riverbed frequently shifts according to the water’s whims, is in some respects notional. Of course, no one is proposing that a wall be built in the middle of the river, or for that matter on Mexican soil, even if Mexico is going to pay for it. So the wall would go on the American side, some distance from its banks—miles into U.S. territory, at times. It would cut people off from their own property and wildlife from the main (and sometimes the only) water source in a vast upland desert. The Center for Biological Diversity has determined that ninety-three listed or proposed endangered species would be adversely affected. The wall could disrupt the flow of what meagre water there is, upon which an ecosystem precariously depends. And it would essentially seal the United States off from the river and cede it to Mexico: lopping off our nose to spite their face. It would shrink the size of Texas.

There is also the matter of efficacy. The wall would probably delay a hypothetical crossing by a few minutes, depending on its design and the manner of the breach. There are videos of Mexicans deploying ladders, ramps, ropes, welding torches, and tunnels to get over, through, or under border fences. (There are about seven hundred miles of fence already, most of it in California and Arizona.) For a great deal of its length, the river is insulated on both sides by hundreds of miles of desert—inhospitable terrain that does more to discourage smugglers and migrants than a wall ever could. (The vast majority of hard drugs intercepted on the southern border is coming through so-called points of entry—the more than forty official crossings—hidden in vehicles and cargo.) And, while the banks of the river, for much of it, are free of impediments, except for thick stands of invasive cane and salt cedar, which can make life miserable for the Border Patrol, about a hundred miles of it cut through deep canyons far more imposing and prohibitive to a traveller on foot than a slab of concrete or steel. The canyons don’t require funding from Congress.

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