Molinaseca is located at 42o 32′ 17″ north latitude and 6o 31′ 11″ west longitude.
It is located in the region of El Bierzo, province of León, community of Castilla y León.

It borders Congosto and Castropodame to the north and east, and Ponferrada and Salas de los Barrios to the south and west. Its southeastern end marks the border with the municipality of Santa Colomba de Somoza.

Most of Molinaseca is on the left side of the river Meruelo, which here opens its lung until now compressed in narrow gorges and cliffs.

The Meruelo river, also called Miruelo, is formed by the streams that flow down from the Dos Hermanas mountain, the Campocebral hill and the Cabezo mountain and those that run through the Rabanedo valley.

In the vicinity of the Prada pass it changes to the West, receiving the waters of the streams descending from the Bouzas and Compludo valleys and those running along the southern slopes of the Irago buttress and at the Malpaso Bridges those coming from the San Bernardino stream that rises below Espinoso and flows into the Boeza at the point called Las Fraguas, between the villages of Campo and San Miguel de las Dueñas.

When it is really Meruelo, it is from the Puentes de Malpaso (you can visit this natural site by hiking the hiking trail Las Puentes de Malpaso) with the union of the streams Grande (formed by the union of the river Prada and Compludo river) and Pequeño or stream of San Bernardino.

Its hydrographic system is oriented towards the Boeza, which marks its northwestern limit.
The main rivers are the Paradasolana and the Meruelo (Leonese diminutive of the Latin adjective merus = pure, clean) that collect the waters of a large number of streams:
  • Paradasolana receives: El Vendañuelo, El Tejedas, El Fuenteporqueiro and El Valleazores.
  • The Meruelo receives in its origin: The Grande, The Pequeño and The de Las Presas, which converge in Compludo. Further down it receives: El Valdefamelgo, El Valdecarrizo and El Santa Catalina.