In 2000 UNESCO designated Muniellos as a biosphere reserve, the area of which was extended in 2003 to take account of the creation of the natural park.

The core area of the Muniellos biosphere reserve occupies 8,661 ha with the rest of the natural park being regarded as a buffer zone.

In the early years of the twenty-first century there has discussion of how the various biosphere reserves in the Cantabrian Mountains should be managed as a single super-reserve to be known as Gran Cantábrica.

[1] This integration is expected to benefit animals which live in the mountains, such as the endangered Cantabrian brown bear which needs to extend its range in order to build a sustainable population.

Although thousands of people live in the protected area, most of the park is sparsely populated and environmental problems are mainly related to mining activity.