The lamia (plural lamiak) is a nymph-like being of the Basque country of northern Spain. They are associated with rivers and caves. Though their origin is within the Basque culture, but they are found in other parts of northern Spain. For example, they are similar in several ways to the mouras encantadas of neighboring Galicia. They are very beautiful and usually have long hair, which they love to comb with golden combs. Like the damas de agua of central Spain, lamiak often have animalistic traits: most often, webbed feet like a duck.

In Navarra and the Basque country, the term lamia is also commonly used for a sea nymph or mermaid. At the same time, some lamiak function as domestic spirits, helping those who leave them offerings with farm or household chores.

The masculine counterpart of the lamia is the mairu (plural mairuak). They are often described either as giants or as human sized but possessing immense strength. In this, they are comparable to the spriggans of Cornwall. It is said that mairuak built the dolmens of the Basque region. Their wives and sisters are also noted builders, as certain bridges in the Basque country were reputedly built by lamiak.

Other forms of lamia include lamina and amilamia. Other forms of mairu include maire, maide, and mainde.