The Reserve is one of the leading enclaves of dunes along the Cantabrian coastline, given its great landscape, geological, botanical and fauna interest. It stands on the left bank of the mouth of the river Pas, in a peninsula area limited by the Mogro estuary and several adjacent beaches. There exist numerous bird populations, such as the ringed plover, dunlin, grey plover, whimbrel, etc which choose this Reserve as a resting place during their migration. The dunes formed owing to the repopulation of maritime pine (Pinus pinaster) carried out in the mid 20th century. You can also encounter a significant offering of lizards, snakes, vipers and amphibians, such as the midwife toad, and the three varieties of newt existing in the region.