Tucked into the hill country near Coyhaique, the Emperador Guillermo is one of Aysén's lesser-known waters — a modest, glacial-volcanic freestone stream that rarely appears on a first-time visitor's itinerary but rewards those who find their way to it. Brown and rainbow trout hold in tight runs and pocket water, and the same big terrestrial patterns that work the region's open water — foam hoppers, Chernobyl Ants — bring fish up readily in summer, since pressure here is close to nonexistent. It's the kind of river best approached with a local guide, both for finding legal access and for reading a stream that has had far less written about it than its neighbours. Expect small-water tactics on a genuinely wild stream.

• Volcanic glacial