Salt Pans and Salt Marshes

Salt pans, or salt marshes, are shallow basins where seawater or estuary water evaporates under the sun and wind until the salt crystallizes and can be harvested. They represent one of the oldest productive landscapes on the Portuguese coast, combining hydraulic engineering, agricultural cycles, and intergenerational knowledge in a single place. More than an industry, traditional salt marshes are constructed ecosystems: a geometric mosaic of ponds, embankments, and channels that shape entire estuaries and support abundant birdlife.

A Solar Evaporation Technique

Production relies on a simple yet demanding principle: gradually increasing brine concentration until crystallization occurs. Water enters the marsh by gravity, leveraging tidal cycles, and flows through a sequence of compartments — storage reservoirs, evaporation ponds, and finally, crystallization ponds. As it circulates, water evaporates, salinity rises, and impurities settle naturally. The marnoto (the term used in Aveiro; salineiro in the south) regulates the flow, opens and closes sluice gates, and maintains each pond at the right level, typically working from spring to autumn. Tools are made of wood to avoid contaminating or damaging the salt crust, and technical vocabulary — barachas, meios, cabeceiras — varies from one salt-producing area to another.

Traditional sea salt is not manufactured but harvested: it results from the combination of human labor with tides, sun, and wind, with no processing after collection.

The finest product, fleur de sel, forms as a crystalline film on the water’s surface in crystallization ponds and is harvested daily by hand with a tool that never touches the bottom — distinguishing it from coarse salt collected from lower layers.

Geography of Portuguese Salt-Producing Areas

The coast between the Ria de Aveiro and the Guadiana estuary offers ideal conditions for solar evaporation, particularly in the south. Historically, Portuguese salt production has been concentrated in five salt-producing regions: Aveiro, Figueira da Foz (Mondego estuary), Tagus, Sado (Setúbal and Alcácer do Sal), and Algarve (Ria Formosa, Olhão, Tavira, and Castro Marim). Medieval records attest to the antiquity of this activity: documents from the Baixo Vouga mention salt marshes as early as the 10th century, and Aveiro’s salt industry grew alongside cod fishing, which relied on it for preservation.

An exception to this coastal logic is the Salinas de Rio Maior, a rare case in Europe: an inland salt pan, about 30 km from the sea, fed by a well of water seven to ten times saltier than seawater, which passes through an underground rock salt deposit at the foot of the Serra dos Candeeiros. Documented since 1177, they are classified as a Property of Public Interest and remain operational. The salt marshes of the Ria de Aveiro exemplify how this activity has shaped entire lagoon landscapes.

Landscape, Heritage, and Threats

Throughout the 20th century, traditional salt production declined drastically. In the 1960s, over two hundred salt marshes operated in the Aveiro region alone; today, very few remain active, outcompeted by industrial salt and imported rock salt. Abandonment threatens a heritage that is both built and intangible — embankments crumble, and the marnoto lexicon fades without transmission.

Recent revaluation rests on three fronts: recognition of gastronomic quality (with protected designations for fleur de sel from Castro Marim, Rio Maior, Aveiro, and Figueira da Foz), the ecological value of salt marshes as wetlands for migratory birds, and landscape tourism. This typology is part of the broader study of built heritage typologies linked to water and territory, in dialogue with water mills and tidal mills and the vernacular architecture of the coast, such as the coastal thatched huts. Preserving a salt marsh is, ultimately, preserving a gesture: that of the marnoto scraping fleur de sel at dusk, repeating a knowledge over a thousand years old.