Sandbanks doesn't look like a city under siege. There are crowds of people; shoeshine boys are blazing away; the stores are open. I'm left at a dismal hotel overlooking the Magdalena and the seedy waterfront. The river is Colombia's Mississippi, once a commercial and poetic artery in national life, now a deadly morass of twisting channels, sandbars, eroding banks, and wrecks. Garcia Marquez called the river "a swamp with no beginning or end," only "an illusion of memory."

A more prosaic fluid--oil--now rules the region. Sandbanks is dominated by a vast refinery, and greasy smoke billows from three huge venting towers topped by balls of flame. These flares burn all day against the gray sky, like false suns. At night their glow is visible even in the surrounding guerrilla encampments.

In the morning I receive a briefing from Colonel Jaime Martinez, the national police commander responsible for defending Sandbanks itself. "Only half the city is ours," he begins, spreading out a map in his second-floor office and sending for coffee that never appears. Although the national police are actually part of the Defense Ministry, equipped with automatic rifles and armored trucks, and received half of the $300 million the United States sent to Colombia last year, the colonel's thousand men still can't venture into most of Sandbanks's poorer neighborhoods. The streets there are controlled by some 400 ELN urban guerrillas. Right outside the city, 2,000 Colombian soldiers--part of the army's 135,000-man force--are facing four other ELN frentes, totaling 800 men, and FARC also has about 1,200 fighters in the region. There is an obscure third group of guerrillas, the Maoist EPL, which has "only" 500 men and which fights in a loose battlefield alliance with the ELN. And there are also about 1,000 right-wing paramilitaries wandering the zone at night, conducting a dirty war of assassinations, orchestrated and financed by right-wing landowners and drug traffickers.

FARC guards about 100,000 acres of coca in zones across the river, Martinez says, but the ELN doesn't tax or protect the drug business, preferring kidnapping for profit. The paramilitaries themselves are involved in drugs, though. Everyone attacks the oil infrastructure in the region, blowing up pipelines, stealing gasoline for profit (about 60,000 gallons a day), and kidnapping oil workers for ransom. "Oil attracts the guerrillas, who need a way to finance their war, which attracts paramilitaries," Martinez tells me. "At any moment here, there are about 3,000 men fighting one another with lead." Assassinations are constant. "We just had two Sunday," he says. Everything wrong with Colombia is wrong with Sandbanks. The terrain here is a single, swirling battlefield where distinctions among players, plans, and policy goals will be impossible. I ask the colonel what will happen when the United States sends sixty helicopters to aid the Colombian military in its fight.

"Personally, I'm very pessimistic," he replies, "because we haven't won this war in twenty years. The money would be better spent on social programs. On highways. Schools. Jobs. Small businesses. On employment and technology for the countryside. Economic opportunity can defeat the guerrillas. But a military program will increase deaths, increase war, increase civilian displacements, and not bring up peace." The colonel's office is spotless, a gesture of order against the chaos beyond. There is not a single paper in either his IN or OUT tray. I can see my unshaven face in the shine of his desk. "You could send two hundred helicopters and that wouldn't do it," he finally says. On the way out, I realize that he is wearing his watch upside down.

My phone rings at 7:01 A.M. two mornings later. "There's someone at the front desk for you," the receptionist tells me. I throw on some clothes and go out. It is a man I can only call the Contact.(*) We have had several frustrating conversations, vague chats about "political actors" and "persons with knowledge of the situation." I think we are maybe going to have a cup of coffee and another pointless talk, but he looks at me and just says, "Get your cameras."

We march out of the front door, around the block, and behind the hotel, where I am introduced to a man in a white shirt. We shake hands. "You are late," he says, and sets off into a slum. The Contact and I follow, trailing thirty feet behind. A disused path leads down to the river. The man in the white shirt clambers down to the waterline, whistles, and then comes back up. I buy a thimble of coffee with the Contact's money--I've forgotten my wallet--and then a canoe pulls up. It is made of brightly painted planks, twenty-three feet long and three feet wide, with no seats. This is the classic yonsin, misnamed long ago for the Johnson brand of outboard motors that powered the first of these fast canoes.

As I climb in, the man in the white shirt says, "You may have to spend the night." I've been awake for fifteen minutes, so all I can think of to ask is, "With whom?" "La guerrilla," he replies, and the canoe pulls away, leaving the man in the white shirt on the bank.

The Boatman shakes my hand and gestures for me to sit in front. We shoot down the Magdalena at twenty miles an hour, spray flying, the skinny boat dashing behind vast islands and then rejoining the main channel. After an hour we turn up a broad quebrada, or side branch, and then race through an endless series of sweeping bends, leaning into the turns and accelerating in the straightaways.

The early morning sun lights us for five minutes--the sun!--just as we approach a riverside checkpoint sometimes manned by Colombian marines. The Boatman tells me that we are on a bird-watching expedition. Do I understand that? I do. I turn the phrase "expedicion ecologica" around in my mouth, but the government post is abandoned, and we roar past. Then the sun rises behind the clouds again, and we turn into yet another side branch of the side branch. We swing steadily through an ever tighter series of horseshoe bends, the river folding back on itself. We slow and get quiet. There are more agonizing hidden bends, muddy banks that look like ambush posts, and an endless wall of green. It is already hot, and impossible to see much in any direction.

I am let off at a bump in the bank. A little path leads up to a clearing ringed by a high green wall of trees and vines. As instructed, I walk into the clearing, sit down, and then the yonsin leaves. I swat at insects for half an hour and finally build a tiny grass fire for the smoke. This doesn't scare off a single mosquito. There is lots of time to think about bad movies set in the jungle, and then about Garcia Marquez, lingering in his cancer ward, composing lists of all the things that Fidel Castro absolutely never told him. In The General in His Labyrinth, Marquez warned against loitering like this on the banks of the Magdalena: "There were men roaming that desolate place," he wrote, "who were as big as ceiba trees and had the crests and claws of roosters."

Fifteen more minutes and I hear a rustle, and then look over to see a forehead. It turns into a head, and then a camouflage uniform, and then five more uniforms. The six men step out of the brush. They aren't as tall as ceiba trees, and their claws are Galils and AK-47s. They come right over to me, pretending to be relaxed. The first thing they do is shake my hand, one by one, and then stamp out the grass fire.

The guerrillas are in camouflage, with worn webbing that holds radios, rifle grenades, and spare clips. Some of them have shoulder boards in ELN red-and-black, which is a relief: I wouldn't want to run into the wrong set of guerrillas out here. They are all wearing battered leather combat boots and have small green towels draped over one shoulder, which they use to swat at bugs. They leave one man to watch me, and go back into the jungle again. For the next two hours the mosquitoes are on me like NATO on Belgrade, and the guerrillas have clearly picked their dumbest soldier to guard me, fully aware that I will not get one single word out of him. Finally the other five guerrillas reappear.

One of them--a vaguely amused twenty-eight-year-old, who is tall by local standards--searches my camera bag. He has two radios and a codebook, and I finally realize he is the leader. I explain that I am a journalist, that he may have received a message I was coming, that I want to ask about American poli--"Yes," he interrupts. "We had a very nice woman from the Washington Pist one time."

"Post," I blurt out. I can't stop myself. "The Washington Post."

"Pist?" he asks.

"Post.""Yes, the Post. She never sent me the article she wrote. Why do you suppose that is?"

He pats me down carefully, then tells me his real name, but later insists that I forget it. I have to refer to him by his war name, which is Comandante Diego. He is the commander of the ELN's frente sur oriental, one of four in the Middle Magdalena, and is currently orchestrating the siege of Sandbanks.

We get in another yonsin, sitting on the gunwales and packed tightly together, knees interlocked for stability in the tippy canoe. I look down, avoiding their eyes, and study the interspersed pattern of legs: camo, denim, camo, denim, camo. The canoe motors upriver, through smaller bends, and we pick up a second yonsin with two more guerrillas. All the men are silent. I'm thinking about the extremely small possibility (the impossibility, really, if you consider odds and chances and geography) that a new Black Hawk gunship is patrolling over this area. Six choppers--state-of-the-art machines, bristling with rocket pods, miniguns, and other tools for fighting drugs--have been delivered to Colonel Martinez's National Police.

Maybe one of these lethal machines is going to stumble overhead, by chance, and the pilot is going to look down and see two canoes filled with guerrillas. Despite the U.S. pretense of "only" getting involved in fighting drugs, there is only one battlefield in Colombia, and the pilot is not going to pause to see if we are ELN guerrillas or FARC guerrillas, or to inquire whether we take drug money, or to ask if that is a civilian on board. He's just going to lean over the cyclo, drop the ship down fast, and press a button. Sooner or later, in one spot or another, a piece of the American drug war will come hurtling out of the sky looking for these men.