"In the Upper Pleistocene, 100,000 years ago, an impressive glacier with ice tongues of more than 20 kilometres gave rise to the current Sanabria Lake. Today, its 318 hectares of surface and a depth of up to 51 metres make it the largest lake on the Iberian Peninsula.
The most abundant forests in the area around Sanabria Lake are those formed by the Pyrenean oak or Pyrenean oak. There are also some interesting patches of holly and yew, while birch and alder trees are abundant on the banks of the mighty rivers that descend from the peaks or connect the various lagoons located within the Natural Park. As the height increases, the forest is replaced by a thicket of scabbards, berms and heaths. In Sanabria, the famous endemic species are also found: the Sanabria spruce sapling and Geranium bohenicum. Among the fauna, we can mention the golden eagle, the wolf, the roe deer, the Bocage lizard and the Seoane viper.
In addition to its high environmental value, the Sanabria Lake and Segundera and Porto Mountains Natural Park offers valuable historical, artistic and cultural resources. Along with the interesting Romanesque monastery of Santa María, in San Martín de Castañeda - headquarters of the Natural Park Interpretation Centre -, the urban and monumental complex of Puebla de Sanabria and the numerous examples of popular architecture distributed in the towns of the area stand out.
The Tera Canyon
Very close to the shore of Lake Sanabria, in Ribadelago Viejo, begins the route that goes through the narrow and spectacular Tera canyon. At the exit of the aforementioned town and always parallel to the river, you will find the closed gorge. After leaving the San Martín de Castañeda path on the right and fording the Tera through an improvised passage, the path runs through an area of ??large stones carried by the current.
When you reach the first waterfalls, you have to cross the river again and start to gain altitude to overcome the first topographical difficulties. The traces left by the various Quaternary glaciations on the Cambrian rocks of the area characterise the relief. Deep ravines, glacial cirques, highlands, lakes, moraines and erratic blocks are some of the signs of erosion caused by ice. In the privileged setting of the Sanabria Lake Natural Park, up to 40 glacial lagoons can be found.
A path that is increasingly blurred reaches, after descending a natural staircase, the so-called Poza de Las Ninfas. Waterfalls and small lakes alternate, forming a rosary of great beauty. The valley of the Cueva de San Martín is formed in the widening of the gorge. The walker has two alternatives to return, the first is to return by the same path; the second and more laborious is to continue - following the Covadosos stream - to San Martín de Castañeda and link up, by the so-called and well-marked San Martín path, with Ribadelago Viejo.
Vegetation
Sanabria is rich in flora, with more than 1,500 plant species living here. This remarkable botanical diversity is a consequence of its geographical location. The Sierras Segundera and Cabrera constitute the boundary between the Atlantic and Mediterranean climates. Because of this, the different orientations of their slopes, valleys and peaks determine the predominant influence of one of these two environments. The Atlantic predominates on the slopes facing north and west, while those facing south and east have Mediterranean characteristics. To this must be added extreme conditions on the highest peaks, which has led to the existence of unique species adapted to these characteristics. In some cases, these are authentic living relics of the Quaternary that have survived and evolved in isolation on these peaks for more than 10,000 years, such as Ranunculus parnassifolius ssp. cabrerensis or Armeria bigerrensis.
The most widespread species in Sanabria is the oak, Quercus pyrenaica, adapted to the cold of winter and the prolonged dry season, abundant in the Tera basin and in ravines and slopes of the Sierra Segundera. Here it is called "carballo" and has long been an important part of the domestic economy of Sanabria, providing its inhabitants with structures for their houses and firewood for their homes. Along with it, the scrub formations dominate a large part of the mountain, with legumes of the genista genus, heather, mountain broom, etc. standing out, especially abundant in areas degraded by fires or overgrazing.
The chestnut is also a representative species of the Park, although it is very scattered. In the upper and middle part of the Tera there is holly. Yews are also found in ravines and hillsides, mixed with oaks, some of which are centuries old. On the banks of the Tera and on the banks of rivers and streams there are alders, ashes and willows. Throughout the Park you can see rowan, wild cherry, hazel, birch, etc.
The abundance of streams, springs, lagoons and peat bogs allow for the existence of aquatic flora characteristic of clean, acidic and scarcely mineralised waters such as those of Sanabria. Notable for their rarity at such low latitudes are the peat bogs: formations made up of compact masses of different species of Sphagnum moss, some of which have a very limited distribution and are even unique in the Peninsula, and which can reach several metres in thickness.
Fauna
Due to the geographical location of the Sanabresa region, the fauna of the Park is quite varied. There are more than 190 species of vertebrates within the Protected Area. Of these, 7 species of fish find their habitat in the lake, lagoons, rivers and streams. The trout (Salmo trutta) deserves special mention due to the considerable size it can reach in the lake and its exquisite flavour; along with the redfish, chub, barbel, etc. 142 species of birds fly over this Natural Park, of which 17 are diurnal birds of prey such as the golden eagle (Aquila chrysaetos), the honey buzzard (Pernis apivorus), peregrine falcon, common buzzard, kestrel, eagle owl, along with a number of birds, some of which find their most southern distribution in this area, the red-backed shrike, the yellowhammer, the bluethroat. The grey partridge, locally known as "charrela" can be found in the high pastures. Among the oak forests, you can see the common bullfinch, the robin, the jay, the hoopoe, ... Reptiles have more than 10 species in Sanabria, including two vipers: the northern adder and the snouted adder, several snakes: the collared adder, the viperine, the southern smooth snake, the northern smooth snake, etc. The entire area is very suitable for the existence and development of amphibians, given the high number of wetlands; 10 species of amphibians have been counted here, including frogs (barred frog, long-legged frog, San Antonio tree frog), newts (marbled newt, palmate newt) and salamanders (long-tailed salamander and common salamander). As regards mammals, there are 41 species present in this Sanabresa region, the elusive Pyrenean desman, several mustelids such as the otter, the marten, the stoat, the stone marten, the badger, not to mention other larger mammals: the roe deer, the wild boar, the wild cat and, of course, the emblematic Wolf, once the protagonist of tales and legends and today increasingly difficult to see.
Geomorphology
During the coldest phases of the Quaternary, glacial conditions were established in Sanabria that significantly affected the modelling of the mountains originating in the Hercynian Orogeny and rejuvenated in the Tertiary.
The extensive accumulations of glacial moraines throughout the region indicate that the glacial phenomenon had a notable importance and extension here. The limit of perpetual snow has been established at around 1,600 m of altitude, which allowed large accumulations of ice and snow to form on the high plateau of the mountain range during the Würm glaciation, giving rise to a plateau or cap glacier, from which long and powerful tongues of ice diverged, embedded in the former river valleys.
The modifications established by the Würmian glaciation will vary depending on the plateau of the Sierra, where the ice over-excavated the areas of weaker rock, creating small basins in which, when the ice retreated, lagoons were formed, such as Clara, el Cuadro, Mancas, el Payón. Others have been created by damming: Lagunas de Sotillo, la Yegua, Camposagrado, Patos, ... There are also large cirques where lagoons have been established, such as Lacillo. Glacial sedimentation on this plateau gave rise to drumlin-type accumulations.
The valleys remodelled by the glacier have the characteristic "U" shape, wide valleys and deep canyons carved in the hard plutonic rock. The main glacier tongue descended from the Trevinca and Survia cirques, and was embedded in the Tera valley, increasing its thickness as ice from the small cirques and lateral valleys was added. When it reached the current Ribadelago, this glacier tongue was almost 15 km long and more than 300 m thick. Here, the Tera glacier received the contribution of the Cárdena and Segundera tongues, increasing its erosive power even more and excavating the basin that today houses the Sanabria Lake.
The erosive action of the glaciers is combined with an important task of transporting the materials they collect along their receiving basin and which are enclosed in the ice mass or transported over its surface. The main moraine system that the Park houses is located in what was the last stretch of the main glacier; downstream from the Lake, the glacial tongue melted and collapsed, depositing there for millennia and in successive concentric morainic arches, huge quantities of sediments of the most diverse sizes: from earth and dust to large blocks of granite. Most of these moraines are dated as Würmian, although some remains may be older, from the Riss.
10,000 years ago, the glaciation ended and the glacial tongue retreated, revealing wide, deep canyons, hanging valleys, rugged rocks, glacial striations, moraines and the most characteristic element of the Natural Park: Lake Sanabria, the largest lake on the Peninsula and the only one of glacial origin in our country, together with more than 20 lagoons scattered throughout the Sierra.
Landscape
The Park includes the largest lake in the Iberian Peninsula and the only one of glacial origin, with 318.7 hectares and a maximum depth of 51 m, together with numerous lagoons and canyons demonstrating the Quaternary glacial action which, together with lush vegetation of great variety in all its strata and countless waterfalls, streams, etc., makes this area have incredible aesthetic and landscape values.
Values that justify its declaration
It was created in 1978 with the main objective of preserving the morphology sculpted in its rocks by the Quaternary glaciers, the richness of its flora and fauna and the purity of the waters of the only glacial lake in the Iberian Peninsula and of the more than 20 lagoons that make up, after the Pyrenees, the most important group of lagoons in the Peninsula. This entire geomorphological framework is a living book where one can study a phenomenon that, like glaciation, is very far away in time and distance."
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