But that's not going to happen until Mexico goes straight, cleans up its justice and banking systems. Even some American borderlanders who cheer integration in public go off the record to talk about what's wrong, admit that they rarely visit the other side or whisper quietly that they haven't felt the same about the place since a friend's car was hijacked a few years ago, and they never saw him again. You can sense the same mysterious half silence no matter where you go; Mexicans call it Article No. 20, as in, which of the $20 is for me? Police and Customs people pay for their government jobs so they can get in on the mordida, the payoff system. Midwives in Brownsville, Texas, sold thousands of birth certificates to be used as proof of U.S. citizenship. The Arellano Felíx brothers, the Tijuana drug kingpins known for torturing, carving up and roasting their rivals, are paying $4 million a month in bribes in Baja California alone, just as the cost of doing business. The $4 million reward for their capture is one of the highest the U.S. has ever offered, and something of a bad joke under the circumstances. There hasn't been a single nibble in four years. What good is the money if you're dead?

And as lucrative as the drug-smuggling business is, the people-smuggling cartels are prospering as well. The more the U.S. cracks down on illegal immigration, the more expensive crossing becomes. The border patrol has a mission impossible: no matter how many surveillance cameras and motion detectors it installs, still the immigrants come. It's harder to cross and easier to die trying. In some ways it's the lucky ones, say the border agents, who get caught. "Everything out here will either bite you, burn you or arrest you," says the Rev. Robin Hoover, of the First Christian Church in Tucson, Ariz. The Mexican government is considering handing out survival kits, complete with snake-bite antidotes and rehydration tablets, for people intending to set out across the desert—a plan U.S. officials think amounts to an official blessing for breaking American law.

Up and down the border, everyone skirts the fence in his own way. A professor in south Texas says he pays someone $50 a month to smuggle his mom over in a boat for Sunday dinners. He doesn't worry, though, because a federal agent down the street does the same for his housekeeper. "Trying to stop this migration is like trying to stop a wave with a Dixie cup," says Raul Berrios, whose wife Karen runs the popular Renaissance Cafe in Bisbee, Ariz. "It's going to be impossible." There is a whisper network in Bisbee, of codes and messages telling weary crossers where they can stay, safely hidden from the border patrol.

Sometimes nature lends a hand. Highway 4 through Brownsville ends with a stop sign that needs to be taken seriously. The asphalt turns into beach and leads straight into the sea. But turn right, and you can drive down the beach like the old days at Daytona, on fine, hard-packed sand, hugging the Gulf of Mexico. It's a place to appreciate a pristine view: no condos, no concession stands, no concessions at all to anything except the fact that the border begins where the Rio Grande pours into the sea, and so it has to be guarded carefully.

For the first time in 500 years, the river is so low that it just dries up altogether about 50 ft. from its destination and turns into a salt flat. Two alien weeds, hydrilla and hyacinth—border officials don't know how they got there—are growing so fast they have blocked the flow of the river. Fighting them would require approval from both sides, which is practically impossible to get. And so here, all that is left of the border are four metal stakes in the sand, tied with orange ribbons whipping in the gulf breeze.The border patrol has had to make a little sand berm to keep the smugglers from just driving across. The Mexicans, in their window-darkened Pontiacs, drive right up to the very sticks themselves, and the border patrolmen in their Suburbans get out their binoculars, look across the beach and wait to be relieved at midnight.

Just at the moment when, all up and down the river, cities are arguing about where and whether to build more bridges, haggling over diplomatic papers and environmental clearances and political payoffs, all in order to build another truck bridge over a creek—here, nature just went ahead and did it, all on its own.

—Reported by Hilary Hylton/Laredo, Tim Padgett/El Paso, Julie Rawe/New York, Elaine Rivera/Nogales and Cathy Booth Thomas/McAllen