On the final morning of a weeklong fly-fishing adventure to Patagonia last December, I finally found my white whale. In the preceding days, I had fished all manner of beautiful rivers and lakes and caught (and released) more than my share of fish . But I had yet to land anything truly special — a trip-maker — and this creature appeared to be just that.

My guide , an American expatriate named Monte Becker, his colleague, Hayden Dale, and I were on the Paloma River, a renowned trout stream in central Chile. We had begun the day by navigating a series of Class III rapids, then catching a handful of brown trout and rainbow trout that would have been considered whoppers on most other rivers, but here were just the latest in a series of ho-hum catches measuring 18 inches or more.

Just before lunchtime, we ran a stretch of white water that squeezed between a pair of enormous boulders, then opened into a small, hidden canyon. With its overhanging granite walls, moody light and silty water the color of sapphires (if the sapphires had somehow been electrified), the chamber bore traces of both the real-life Blue Lagoon and the fictional Middle-earth. It was one of the most striking spots I’ve seen, on or off a river.