The Gresso river is a tributary of the Vouga and originates at the top of the Arestal mountain almost at 800 meters of altitude. This river runs, in his descent to its outfall, no more than 7 miles, having a total gap of more than 700 meters high. It is, therefore, a mountain river with many cascades and waterfalls, with little flow in summer, only filling with the winter rains. There are two waterfalls that stand out in its path, one below Sanfins village accessible by PR10 – Trilho do Gresso, and the second is located upstream of the bridge between Sanfins and Mouta villages. The cascade of the Gresso, or the cascades of Gresso, are the least well-known in Sever do Vouga, and lead us to the discovery of a dusky river, with a very closed and peculiar riparian gallery.
The sweet chestnut, memory of past times when the mixed woods dominated the valley of the Gresso river, remains on the path that leads to the waterfall. Today the banks are dominated by plantations, but near the river is still a natural large sized tree woods, habitat of the fire salamander and the iberian emerald lizard, species of vivid colors for very different reasons: the defense, in the case of salamander (the yellow is a warning color for predators, since the salamander is tacky); the seduction, in the case of the lizard, since the male bears blue colors at the time of mating to win the female. The european hedgehog also inhabit these woods, but his defense stands pointed in their backs. The iberian frog and the white-throated dipper share the bed of the river, where they receive occasionally the visit of the otter.
The Marco/Estela of Carvalhal (stele) is a granitic monolith that is located on an advanced spur into the southeast part of the Arestal mountain, next to Carvalhal. Serves the functions of mark of territorial boundary between the counties of Sever do Vouga and Vale de Cambra, standing on the dividing line that rises toward the plateau of Arestal mountain to meet the mark inserted in the wall of the St. James chapel (Menhir of Lameirinhos). It is a block of granite with more than 1 meter in height and width on average of 0.5 meters. In face towards the road it has alphabet motifs recorded. Its ancestry is difficult to measure, since the stone work may have widely different ages.
