Declared a SCI (Site of Community Importance) as part of the Natura 2000 Network, it has an area of 1,537 ha and encompasses the municipalities of Agolada, Lalín and Vila de Cruces. It extends along the slopes of the middle and lower stages of the valley of the River Arnego until it joins the Portodemouros reservoir, on the River Ulla.
It is the main representative of the Atlantic forest with Mediterranean influence in the basin of the River Ulla. As the most representative species, the oak and cork trees stand out. We can also see the presence of alder trees along the riverside.
The area features a rich variety of fauna, including a wide range of species linked to scrubland and riverside woodland.
Here we can find a natural swimming area at Ponte Vilariño, where there is also a recreational area and a thermal spring among the ruins of an old spa.