Pozo Tremeo

Pozo Tremeo is a small lake in Rumoroso, a village within the municipality of Polanco, on the coast of Cantabria, northern Spain. It is often described as the only permanent natural lake found along the Cantabrian coastal strip, tucked among meadows and woodland just inland from the sea. The site sits inside the boundaries of the Costa Quebrada UNESCO Global Geopark and has been protected since 2016 as an Área Natural de Especial Interés (ANEI) — at the time only the second such protected area to be designated in Cantabria, after La Viesca.

What is the story behind its name?

"Tremeo" comes from a Latin root meaning "to tremble." The lake formed when a section of limestone bedrock collapsed underground, a classic karst process, trapping water in the resulting hollow. Because the ground around the shoreline remains geologically unstable, visitors walking close to the water can sometimes feel it shift slightly underfoot — the origin of its nickname as "the lake that trembles." Local folklore has grown around that phenomenon for generations: tales of lovers who were never parted, wishes said to come true after touching the water, and rumors of underground tunnels connecting the lake to the sea.

What will you see there?

The lake itself is modest in surface area but unusually deep for its size, reaching down several meters more than one would expect from such a compact karst pool. It is ringed by a mix of deciduous woodland and damp meadowland typical of inland Cantabria. The area is a refuge for species tied to both water and forest habitats, including bats, beetles of conservation interest, and the native freshwater crayfish — a species particularly sensitive to water quality, whose presence is generally taken as a sign of a healthy ecosystem. A footpath circles the lake, allowing visitors to walk its perimeter and take in the view from several angles and shoreline heights.

In recent years, regional authorities have carried out conservation work at the site, including measures aimed at preventing flooding and safeguarding the protected ANEI area — evidence that the lake is actively managed rather than simply protected on paper.

How do you get there?

Pozo Tremeo lies in Rumoroso, part of the municipality of Polanco, on the central stretch of the Cantabrian coast. Polanco sits along the main routes connecting Santander to the western part of the region, making the surrounding area a convenient base whether you are coming from the coast or from further inland. Given how understated the site is, it is worth checking local trail signage on arrival — this is a destination for a short, quiet walk rather than one built around heavy tourist infrastructure.

When is the best time to visit?

Since Pozo Tremeo is essentially a nature spot — woodland, meadow, and the lake itself — it rewards a visit outside the height of summer, when the light and vegetation are best suited to an unhurried walk and the area is quieter than the well-known beaches of the nearby Costa Quebrada. It suits travelers looking for stillness and a lesser-known, inland side of the Cantabrian coast rather than a typical beach outing.

Frequently Asked Questions

Is Pozo Tremeo really the only lake of its kind in Cantabria? It is generally described as the only permanent natural lake along the Cantabrian coastal strip, which makes it a distinctive geological feature in the region.

Why is it called the "trembling lake"? Because of its karst origins and the instability of the ground around its edges — the earth near the water can genuinely shift slightly, a phenomenon that has fed local legends for centuries.

Can you swim in Pozo Tremeo? Available sources do not list swimming as a typical activity here; the site is mainly visited for walking and nature observation, and its ANEI protected status comes with restrictions designed to safeguard the ecosystem.

Is there a marked walking trail around the lake? Yes, a footpath runs around the lake allowing visitors to circle it and view it from different points, though it is a local walking route rather than an extensive signposted trail network.