Amazon immersion: Guests at treetop eco-lodge explore untamed river.

Byline: Richard Scheinin

ON THE RIO NEGRO, BRAZIL _ I was fortunate while in the Amazon to have Michael Kartwright as my guide. Before I flew to Brazil, an old acquaintance _ an expert on Amazonian flora, fauna and religious practices _ had told me that Kartwright was my man. Ex-gold miner, ex-diver, and ex-cowboy _ a "legendary Third World fixer," my friend said, a man who would open doors, take me anywhere I wanted to go, and, best of all, educate me about what I was seeing. I envisioned Kartwright as some kind of wild man.

But here he was aboard a small ferryboat chugging from Manaus, the Amazonian metropolis of 2 million, toward a distant portion of jungle, and he was instead the epitome of erudition and charm. He was 51, a spark plug of a man. Born in Guyana to parents of East Indian descent, he spoke in a clipped staccato rush that reminded me of rapid rhythms coaxed from a tabla drum by a master musician.

Crossing the Rio Negro, which seemed wide as an ocean, he held forth on Amazonia's geologic history, on tectonic plates and tributary sources, on indigenous tribes, dolphins, reptiles and fish, including the 500 types of catfish that swim the rivers here. Cracking open a couple beers and handing me one, he said cheerily that the largest catfish is the piraiba, which can grow to more than six feet and has been known to drag swimming children to the bottoms of rivers and swallow them whole. Kartwright also explained why I wasn't being consumed by mosquitoes: The Rio Negro's waters, dark as leather, are loaded with decaying vegetative matter and tannic acid, which makes it hard for the bugs to survive.

This absence of bugs was delighting me as was the temperature _ a righteous heat, cleansing but not killing _ as we passed through the Rio Negro's narrowest strait and approached our destination. There it was, straight ahead: the Ariau Amazon Towers, a treetop hotel rising from the jungle canopy.

It was about the strangest thing I'd ever seen: five circular towers that resemble lopsided wedding cakes, topped with tin …