Rias

Rias (singular: ría) are drowned river valleys that have been flooded by rising seawater to form long, narrow estuarine inlets. The term is commonly used for features along the Atlantic coasts of Europe, especially in Galicia, Spain, and northern Portugal, where a network of rías defines much of the coastline and the regional landscape.

Formation and characteristics: Rias arise when sea level rises after glacial periods, inundating preexisting river valleys carved into bedrock. The resulting inlets typically extend inland in a branching pattern and contain shallow estuarine basins, tidal channels, and adjacent salt marsh or mudflat areas. They differ from glacial fjords in that they are formed largely by riverine erosion and subsequent submergence, and they often have more sinuous, less dramatic profiles.

Geography and examples: The best-known rías are found in the Rías Baixas of Galicia, Spain, including the Ría de Arousa, the Ría de Vigo, and the Ría de Muros e Noia, as well as the Ría de Ferrol. Similar systems occur along the northern Portuguese coast and contribute to a distinctive coastal landscape across the region.

Ecology and use: Rias host brackish-water ecosystems rich in biodiversity, with tidal flats, salt marshes, and various estuarine habitats. Their sheltered waters have historically supported fishing and, in many cases, aquaculture, notably shellfish farming. They also attract tourism due to their scenic coastlines, seafood cuisine, and cultural landscapes.

See also: The term ría is a regional designation used in Iberia; in other Atlantic regions, similar drowned-valley estuaries may be described with local terms.