A short hike leads from The Slide to the White River waterfall

Len takes off in a spray of river water

In the middle of the action

Trying hard to stay in the boat

Whitewater roars as the raft hits a hole in the river. The front of the boat goes down, and then pops back up as the raft executes a vertical U-turn at the bottom of the hole. The directional quick-change is too much for the two teens in front. Adrian-a Panamanian from the capital-and his American cousin Kevin go flying into rapids, and shoot out ahead of the raft. Both manage to wash up, forcefully, on a rock in the middle of the river, but the raft is heading straight for them. They let go a split second before the leading edge of the speeding rubber craft would have pulped them against the rock.

Our guides had known that the Big Stick rapids would be challenging, so Len, the slight Panamanian teen who serves as our kayak safety guide, was on the shore with a line ready to throw to the two guys in the water. They both catch the line and Len hauls them in like a pair of oversized fish. Minutes later, the two climb back in the boat, which is now drifting in calm water below the rapids. White ichor drips down Adrian's left leg.

Looking shaken, Adrian puzzles over his leg for a moment. He discovers that the force of the blow against the rock had broken open a tube of sunscreen in his pocket, our second equipment casualty of the day. "For a minute there, I thought I had vomited and didn't realize it," he says.

Tiny, the raft guide, teases him. "I thought you were so scared your blood ran white."

Rafting Panama's Rio Chiriquí Viejo is reminiscent of that cliché description of war and air travel-long periods of boredom punctuated by moments of terror. The analogy is not perfect, because the canyons and rainforest surrounding the river are far too beautiful and impressive to allow for boredom during calm period between rapids. The adrenaline rushes, however, are very real on some of the rougher stretches of water.

Our first equipment casualty came after less than 10 minutes on the river. I was in the raft with the two teens, Adrian's father Ricardo and Tiny, the guide. Tiny's real name is Victor Avila, but his nickname is fitting. He only stands about five foot six, but he has a voice that is meant for being heard over roaring whitewater. We were all still getting used to each other and getting reacquainted with being on the water after a long absence when we hit the Brazilian, the first set of rapids.

"Adelante, adelante!" shouted Tiny, then "Derecho atras, derecho atras", urging us first to paddle forward and then directing the right side paddlers to reverse gears to spin the boat around. We were all a bit slow to react to the instructions, however, so we hit a big bump and three of us went into the water, including the guide. I was still a little freaked out by the alarming liability waiver that I had had to sign at the crack of dawn, which contained all too many synonyms for "death" and "dismemberment". Consequently, I grabbed at my first chance to get back in the boat (which just happened to be the trailing arm of the raft guide, who got to the boat before I did). It was then I felt my Teva slipping off my left foot, but lured by the promise of reaching relative safety, I didn't stop to resecure the Velcro strap. The sandal came off as my foot left the water.

"Sorry about your Teva, man," said Len. He is reputed to be one of the best kayakers in the country, but he's still just a kid. After retrieving a pair of paddles, he hung upside down in his kayak for what seemed like an unhealthy amount of time fishing for my sandal in an eddy just downstream from the Brazilian. "This river's taken a lot of Tevas." In June, although the rainy season has well begun, the Rio Chiriquí Viejo is not yet running at full capacity, so there are plenty of exposed boulders to negotiate on your way downstream. Tiny said that in these conditions, it is a Class III river with some Class IV rapids.

The Chiriquí Viejo is born high in the Cordillera Talamanca, near the western border of Panama. Perhaps the easiest way to get there is to fly Aeroperlas from Panama City to David, the capital of Chiriquí Province. David lies on the coastal plain, and it is popularly know as "The Oven". It is always hot and sticky. Many visitors prefer to leave the town and head for a more pleasant climate in the mountains as soon as possible.

We started our trip bright and early at the office of Chiriquí River Rafting in Boquete, a pretty little mountain town in Chiriquí Province. Hector Sanchez, Chiriquí River Rafting's general manager and chief guide, gave us a safety talk before asking us to sign those waivers that so alarmed me. Sanchez, a 60ish native Panamanian, is a 25-year veteran of the US military, where he worked as a civilian recreation and outdoor activities organizer. Chiriquí River Rafting, founded in 1995, has never lost a customer, but Hector reminded us that whitewater rafting remains a risky undertaking.

"You gotta move quickly when you hear 'high side', or you could wrap the raft around a rock and it could be pinned there by the force of the water entering the boat," he said. "Then we have a situation where the river is on the boat, rather than the boat being on the river. We also have a group of rafters trapped on a rock like a bunch of penguins."

He went on to show us the proper way to throw a line to somebody in the water, and the proper way to hold your body when you are the one being swept downstream. After the formalities were taken care of, we all climbed into an immense four-wheel-drive van, with the raft and a river kayak strapped on top. Boquete lies only about 20 miles from the Chiriquí Viejo put-in, as the crow flies. That crow, however, would have to fly over or around Volcan Barú, the highest point in Panama at 11,400 feet. There are no roads in that area. Instead, we had to drive about 25 miles south to David and 40 miles west to the border town of Paso Canoas.

About 40 minutes up a steep and narrow road north of Paso Canoas, Chiriquí River Rafting maintains a put-in site on Rio Chiriquí Viejo. Guides stow and secure what they can in the raft and then toss it down a nearly vertical 1000-foot slope. The raft rides a cushion of crushed vegetation and mud all the way to the rocky bank of the river, while rafters make their way more gingerly down a switch-backed trail that remains plenty slick.

We put in at about 10 in the morning, and stayed on the river 2 hours before breaking for lunch at a waterfall the guides called "El Deslizador" (the slide). Here, the Rio Blanco runs nearly 100 yards down a granite face canted at about 45 degrees. Len, who was staying behind to make lunch, lent me one shoe (which unfortunately was about one size too small), to make a 10-minute hike up the Rio Blanco to another waterfall.

The hike was challenging, as the trail at times was nearly vertical and at other times wound in and out of the slick stony bottom of the river. Wearing one Teva and one too-small tennis shoe didn't help matters. The goal was worth it, however. At the end of the trail lay an immense cascade. It must have been 30 yards tall, and the drop was perfectly vertical. Tiny stripped off his shoes and led us across a pool at the bottom to where the falls entered the water. Crash helmets still on, we sat on natural seats notched into the rock under the deafening spray for 10 minutes or so. I worried briefly about falling tree trunks, but nothing happened.

After lunch we spent another two hours on the river, crossing rapids like the Son of a Bitch and The Three Jumps, as well as the Big Stick where Adrian's blood ran white. The last hour of the ride was pretty calm, and we had more time to admire the scenery and the fauna, which included fishing cormorants, river otters and Jesus Christ lizards, comically impressive when they are running across the water.

Some five hours later and 16 miles downstream from the put-in, we climbed back out of the river. Len lent me one shoe again to make the very steep and rocky five-minute walk back to the van. We had to disembark on the wrong side of the river, as the side where the van was parked was a nearly vertical rock face, about 15 feet high. We made our way over a rotten wooden bridge crossing the river. Great gaps between the wooden planks allowed us to see where the iron support struts ran underneath. Tiny said it would be a good idea to keep our weight on the iron, and I couldn't argue with that.

When we got back to the van, the rafters all changed into dry clothes while the driver loaded up the raft and all the gear. I rode all the way to Paso Canoas with one bare foot. Luckily for me, Paso Canoas is a popular destination for Costa Ricans to slip across the border for a bit of shopping. Brand name warehouses line the narrow main street, and we stopped at the largest so I could buy a new pair of shoes.