The Malleo is actually a big spring creek. It flows out of Lake Tromen as a very small free-stone mountain stream. Once it hits the beautiful Malleo Valley, the river starts receiving spring water from numerous tributary spring creeks including the Huaca Mamuil, the Mamuil Malal, the Tres Picos and several others.
Virtually 90% of the Malleo River water is spring water. This unique feature makes for a river with consistent water temperature and stable conditions. Hence underwater life is rich and varied, from profuse insect life (nymphs, larva, pupa, mayflies, caddis and stoneflies) to countless terrestrials and “pancora” crabs. Thus this rich aquatic life has enabled the Malleo to have one of the healthiest populations of Brown and Rainbow trout in Northern Patagonia.