The Malleo river rises at the Tromen lake, originated by the melted waters of Volcan Lanin Glacier. This ice-cold waters, rich in minerals, provides an appropriate environment for a huge variety of insects, reason why Malleo is distinguished worldwide for dry fly fishing.

Stream conditions vary between slow flowing in the upper meadow areas and faster waters on the lower reaches, surrounded by willow lined banks which arise perfect conditions for dry fly fishing.

Trouts are sensitive to hatches which occur regularly throughout the season; caddis, stoneflies and small terrestrials in the early season and mayflies toward the end, March and April. During clear weather days, surface activity on the Malleo an anglers dream come true. The size of these fish is between 15 and 17 inches, some may grow up to 24+; it´s not rare for an anglers to land from 6 to as many as 40 fish on a good day.