The Liencres Dunes are one of the most important dune systems in northern Spain. They are located on the center of the Cantabrian coast, above the right bank of the mouth of the Pas River. The Natural Park of the Liencres Dunes was dedicated in 1986, occupying a total area of 256 hectares.
The Liencres Dunes owe their formation to wind action, which gathers sand from the coast and sand from the final section of the Pas River, the Mogro Estuary. Thus, large dunes are formed and arranged into various ecosystems depending on the mobility of their sand. There are mobile dunes and stationary dunes classified by different states of mobility according to the amount of vegetation that covers them, with dunes farther from the coast having denser vegetation. The Pas River is the backbone of the Liencres Dunes, containing several coves and the beaches of Valdearenas and Canallave.
In general, the Liencres Dunes have scarce and bushy vegetation that is adapted to the area’s saline ground. The park is home to some species of interest: several types of orchids, strawberry trees, and jarillas, unusual on the north coast of Spain. During the second half of the 20th century, the pine forest began being reintroduced, and it currently occupies a considerable section of land, accompanied in some spots by oak trees. The coast of the Liencres Dunes has some communities of marine birds, such as seagulls, calidris, avocets, and other species that stay for the winter, like herons and cormorants. Mammals are scarce and include various kinds of small rodents and bats.
The Liencres Dunes have large parking lots and two marked routes. The first route goes through the beaches and the dunes until arriving at the mouth of the Pas River, while the second route goes through the pine forest and skirts around the dune area.
The entrance to the park is marked on the CA-231 highway. The CA-231 can be easily accessed by the A-67 highway, which joins Torrelavega with Santander, a city found right nearby the dunes.