Pas–Miera Basin: Rivers from Different Valleys

Hydrological planning groups the Pas, the Miera and other coastal watercourses in a shared water-management system. This does not mean that they all flow into one another: the Pas and Miera have separate basins, while several coastal rivers flow directly into estuaries or the Cantabrian Sea. This page organises the system’s main watercourses and distinguishes physical connections from administrative grouping.

Riverside path on the Miera at Mirones. Photograph by Valdavia, CC BY-SA 4.0 licence (licence). Wikimedia Commons file.

The Pas River and its tributaries

The Pas rises around Pie de Castro Valnera and Peñas Negras in Vega de Pas and reaches the Mogro estuary. The Pisueña is its main right-bank tributary; the Magdalena River joins from the left.

• Pas River ES: Pasiego headwaters, Toranzo valley and outlet to the Mogro estuary.
• La Pila River ES: rises at the spring of the same name in San Martín de Toranzo (its upper course is called Juanas stream), receives Troneda stream according to municipal planning and flows into the Pas at Santiurde.
• Sonoro River: small watercourse mapped in Resconorio, Luena. Regional connectivity assigns it to the Pas system, but its direct confluence and exact headwaters remain unverified.
• Pisueña River ES: from La Garma and Selaya through the Carriedo valley to its confluence with the Pas at Vargas.
• Seco de Selaya River ES: documented Pisueña tributary upstream of its confluence with the Pas; its exact source and the variant name “Valvanuz River” need confirmation.
• Rubí River: mapped watercourse in Abionzo, cautiously assigned to the Pisueña system; a possible connection with Rubionzo remains unresolved.
• Junquera River ES: flows through Villacarriedo from the forested headwaters at Hayal de Aloños to the Pisueña. Santibáñez Flour Mill documents its use for water power. Its precise source, tributaries and relationship with Morell stream need confirmation.
• Llerana River ES: flows through Saro from the eastern slopes and joins the Pisueña; its exact headwaters and named tributaries remain to be verified.
• Campillo River ES: Pisueña tributary in Selaya; its headwaters are located around the Campillo neighbourhood, but no exact spring is confirmed.
• Parayas or Suscuaja River ES: rises on the northern slope of the Matanza range near Esles, crosses the Cayón valley and flows into the Pisueña. Its course is also locally known as Suscuaja.
• Magdalena or Luena River ES: descends from the Escudo and Magdalena passes through the Luena valley and joins the Pas at Entrambasmestas; minor tributaries need individual verification.
• Aldano River ES: Pasiego watercourse in San Pedro del Romeral and left-bank tributary of the Pas; its precise source, named tributaries and access to its waterfalls remain unconfirmed.
• Barcelada River ES: flows through Barcelada and Bustaleguín valleys, with old mills and waterfalls; it is a left-bank tributary of the Pas. Its headwaters are narrowed down to the area between the source and Burnalón Mill, but the spring and named tributaries still need checking.
• Troja River: crosses the Pasiego valley of San Pedro del Romeral and flows into the Pas; its best-documented named tributary is Jaral stream.
• Yera River ES: rises at Estacas de Trueba and reaches the Pas at Vega de Pas. It receives Aján stream, whose banks and waterfalls have a municipal route; the former PR-S 75 is no longer officially approved and lacks maintenance.
• Viaña River of Vega de Pas: left-bank tributary of the Pas, with historical headwaters at the springs of Marruya and Peñalasa. Do not confuse it with the Viaña stream in Cabuérniga, which belongs to the Saja system.
• Carrimont River ES: short course through Parbayón and Renedo that joins the Pas upstream of Quijano; its exact source and named tributaries remain unverified.

The Miera River and its tributaries

The Miera descends from the area around Lunada Pass towards Liérganes and the Cubas estuary. Its tributaries include the Aguanaz and Pámanes, which enter from opposite banks.

• Miera River.
• Carbajal or Carcabal River ES: Miera tributary near the protected Puyo area; its exact headwaters, confluence and named tributaries remain to be confirmed.
• Aguanaz River: rises around El Suto and receives the substantial karst flow from Fuente Aguanaz; it crosses Entrambasaguas and Hoznayo and joins the Miera at Villaverde de Pontones.
• Revilla River or Revilla stream: a 5.34 km water body in Riotuerto; it passes La Cavada and joins the Miera. Local sources link the name Covadal to the valley, but that identification needs confirmation.
• Pontones River: flows through Ribamontán al Monte, with springs associated with Omoño and Sopenilla; it receives Vía stream and joins the Miera at Villaverde de Pontones. Its official water body is 10.02 km long; no single exact source has been identified.
• Pámanes River ES: rises in the Somo range and descends through Pámanes and El Condado to the Miera. The basin study measures it at 9.6 km; the “Pámanes stream” water body in the management plan has a different boundary.
• Penagos River ES: a mapped 2.44 km course in Penagos, geometrically linked to the Pámanes; records document mills and dams from 1638. Its source and the precise hierarchy of the confluence remain unconfirmed.

Coastal basins included in the system

• Mina River ES: crosses Villaescusa, receives Obregón stream according to the Cantabrian Official Gazette and reaches the Mina channel and Solía estuary. The hydrological water body groups both courses and does not by itself establish the length of each one.
• Herrera River ES: coastal watercourse in Ribamontán al Mar, passing Carriazo and flowing into Galizano estuary. Official sources vary in naming the Colina ravine; its source and tributaries need more precise documentation.

The Pas–Miera system used by the Hydrographic Confederation also includes coastal watercourses and basins beyond those of the Pas and Miera. Their direct outlets are not presented as tributaries of those rivers. The guides to Campiezo/Campiazo, Herrera, Mina and other listed watercourses are linked in this index; each retains specific uncertainties about basin boundaries, sources or tributaries when the available documentation is inconclusive.

• Campiezo or Campiazo River ES: rises around Regolfo in Solórzano, crosses Hazas de Cesto, Beranga, Escalante and Meruelo, and flows into the Ajo estuary. It has its own coastal basin, although it belongs to the administrative Pas–Miera system.
• Fuente de la Virgen and the source of the Campiezo ES: a historic guide retained as a local reference; its title is not treated as proof of a single spring.

Sources for the organisation

• Cantabrian Hydrographic Confederation, Water Resources Inventory, Pas–Miera system.
• Cantabrian Hydrographic Confederation, flood-risk maps for the third planning cycle.

Existing guides and routes

The historic URLs of these pages are retained. Availability, trail conditions and local restrictions may change.

• Source of the Pas River and the Pandillo valley ES.
• Bridge over the Pas ES and the Pas at Puente Viesgo.
• Source of the Aguanaz at Entrambasaguas ES, part of the Miera system rather than a source of the Pas.
• Rubionzo River and Zarrizuela oak grove ES: its possible identity with the Rubí has not been confirmed.