The hot springs of Uruguay: the oil nobody found
In 1957, ANCAP technicians drilled the north of the country looking for oil. Out came water at 39 degrees. Today it is the thermal region, mapped by science.
In October 1957, technicians from ANCAP — the Uruguayan state oil company — were drilling the north of the department of Paysandú in search of oil.
They did not find any.
What came up the well was something else: a spring of crystal-clear water, loaded with minerals, at around 39 degrees.
At the time, that was recorded as a technical failure. Today it is one of the greatest natural assets of the region and the economic engine of two cities — and Uruguay has just mapped scientifically, for the first time, exactly what is inside that water.
Where it is, and why it is there
The Uruguayan Thermal Region occupies the north-west coast of the country, in the departments of Salto (136,197 inhabitants) and Paysandú (121,843), on the Uruguay river and facing Argentina.
The explanation is geological and worth understanding, because it is what guarantees the resource will not run out.
The water comes from the Guarani Aquifer System, one of the largest cross-border freshwater reservoirs in the world: around 1.2 million km² spread across Argentina, Brazil, Paraguay and Uruguay.
Within Uruguayan territory, the aquifer outcrops at the surface in the east, in the departments of Rivera and Tacuarembó, and dips progressively to the west, where it becomes confined beneath the basalts of the Arapey Formation — the same Serra Geral formation known in Brazil. Near the Uruguay river, that basalt layer has an average thickness of around a thousand metres and works as a lid.
That is why the thermal wells of Salto and Paysandú have to go down between 1,000 and 1,400 metres. And that is why the water comes up hot: it circulated at depth, confined, for a very long time.
What science discovered in 2026
Here is the new part, and it is recent.
Researchers from the Universidad de la República and the Universidad Complutense de Madrid spent three years developing the first Vademecum of Thermal Mineral Waters of Uruguay. The first results were presented in June 2026, in Salto, during the First Conference on Medical Hydrology and Thermal Tourism.
The seven thermal wells of the region were analysed. For the first time, the mineral composition of each of them is known — and they are not the same.
The study classified the waters into two groups:
Group 1 — the waters of the Guarani Aquifer (Arapey, Altos del Arapey, Daymán, Aguas Claras, Guaviyú and another well in Salto). Weak to medium mineralisation — dry residue between 311 and 734 mg/L —, temperatures from mesothermal to hyperthermal and a predominance of bicarbonate and sodium, with calcium and magnesium.
Group 2 — Almirón, in Paysandú, which does not come from the Guarani Aquifer: a distinct hydrogeological origin, linked to the crystalline basement and to Devonian sedimentary units. Sodium chloride facies, strong mineralisation — dry residue of 6,590 mg/L — and a lower temperature.
The measured temperatures range from 32 °C at Almirón to 44.5 °C at Aguas Claras, with pH between 7.8 and 8.5.
According to the head of tourism at the Intendencia de Salto, the departmental government, it is the first time this information has been available — which allows hotels and thermal centres to describe with precision the properties of the water they offer.
What these waters indicate — and what still cannot be claimed
Here it is necessary to be rigorous, because the subject attracts easy promises.
The study points, by analogy with comparable international hydrothermal profiles, to principal balneological indications linked to musculoskeletal and rheumatic conditions and to dermatological conditions, as well as emerging indications related to stress, sleep disorders and obesity.
The waters of the first group, of low mineralisation and higher temperature, appear associated with uses linked to atopic dermatitis, stress reduction, improved sleep, muscle relaxation and rheumatological conditions. Those of Almirón, more highly mineralised, are indicated for psoriasis, flotation treatments and rehabilitation processes — with the express caveat that they require more care and professional guidance and are not recommended for prolonged treatments.
And the most important caveat comes from the study itself: the researchers conclude that future research should concentrate on controlled clinical and balneological studies in order to validate specific therapeutic effects. What exists today is chemical characterisation and classification by analogy — it is not clinical proof.
No thermal centre should promise more than that, and neither shall we.
The four centres
Each has its own access arrangements and profile.
Termas del Arapey (Salto). The first thermal complex in Uruguay. It is 80 km north of the city of Salto — km 548 of Ruta 3, plus 19 km along the camino Raúl Gaudín. It has open, covered and semi-covered pools set among gardens, with bungalows, motels and all-inclusive hotel accommodation. Access is restricted to those staying at the thermal centre.
Termas del Daymán (Salto). Km 478 of Ruta 3, just 10 km from the city of Salto — the most urban and the most accessible of the four. It has a range of hotels, a spa, private thermal pools and the Acuamanía water park. The municipal area is open to the general public, with pool temperatures regulated by season. It closes on Wednesdays.
Termas de Guaviyú (Paysandú). The centre born of the 1957 well. An enclosed park of 109 hectares, with 15 pools between 26 and 41 °C, covered and open-air, surrounded by yatay palms and native woodland, on the banks of the Guaviyú stream. It has camping, municipal motels, cabins and private options. Access restricted to guests.
Termas de Almirón (Paysandú). The only salt-water hot springs in the region. The municipal area has salt-water and freshwater pools, bungalows, cabins and camping, with private developments around it. Access restricted to guests.
Why this matters to anyone thinking of living in Uruguay
Three concrete reasons, beyond the weekend.
It is a region with its own permanent economy. Salto and Paysandú together hold more than 250,000 inhabitants and are the two largest cities in the Uruguayan interior. They are not seasonal resorts: they are cities with a hospital, a university, retail and industry — and a tourism sector that works all year round, peaking in winter.
The cost of living is the lowest in the country. This is the coast of the Uruguay river, off the Montevideo–Punta del Este axis and outside the pricing logic of the Atlantic coast.
The pattern of use is long-stay. Thermal spa use is, by its nature, an activity of long and repeated stays — the opposite of seasonal tourism. For anyone thinking about a rental property, it is demand spread across the twelve months.
And frankness is warranted: anyone who depends on an international school, high-complexity medicine or a daily international airport will still need Montevideo. This is a region for those who put cost, nature and pace first — not density of services.
Disclosure note: the hydrogeochemical data, the temperatures, the dry residue values and the classification of the waters come from the study characterising Uruguayan thermal waters conducted by researchers from the Universidad de la República and the Universidad Complutense de Madrid, whose first results were presented in June 2026. The balneological indications cited are classifications by analogy with comparable international profiles; the study itself concludes that controlled clinical studies are still needed to validate specific therapeutic effects. This article does not constitute medical guidance. Information on access arrangements, opening times and services at the thermal centres comes from official departmental sources and should be confirmed before visiting. Population data are from the 2023 Census of the INE, the national statistics office.
Frequently asked questions
Where are the hot springs of Uruguay?
On the north-west coast of the country, in the departments of Salto and Paysandú, on the Uruguay river. The four main centres are Arapey and Daymán, in Salto, and Guaviyú and Almirón, in Paysandú.
Where does Uruguayan thermal water come from?
From the deep circulation of the Guarani Aquifer System, which covers around 1.2 million km² across Argentina, Brazil, Paraguay and Uruguay. In the Uruguayan north-west the aquifer is confined beneath the basalts of the Arapey Formation, and the wells go down between 1,000 and 1,400 metres. The exception is Almirón, whose water has a distinct hydrogeological origin.
What temperature is the water?
The measurements in the 2026 study recorded from 32 °C at Almirón to 44.5 °C at Aguas Claras. At Guaviyú, the 15 pools operate between 26 and 41 °C.
Do Uruguayan thermal waters have proven therapeutic effects?
The 2026 study characterised the seven sources chemically and pointed to balneological indications by analogy with international profiles — chiefly musculoskeletal, rheumatic and dermatological. The authors themselves conclude that controlled clinical studies are still needed to validate specific therapeutic effects.
Which of the hot springs is open to the public without staying overnight?
The municipal area of Termas del Daymán, in Salto, has open access to the general public, closing on Wednesdays. Arapey, Guaviyú and Almirón restrict access to those staying at the thermal centre.
How were the hot springs discovered?
By chance. Oil exploration campaigns in the 1940s and 1950s found thermal water instead of oil. In the case of Guaviyú, the ANCAP drilling of October 1957 brought up a spring at around 39 degrees.
The starting point
There is a fine irony in this story, and it says something about the country.
Uruguay spent decades looking for oil and never found any. It found hot water at fourteen hundred metres down, in a poor region of the north, and turned what was a drilling failure into two cities with a permanent tourist economy — and, almost seventy years later, sent two universities to study exactly what is inside it.
It is the same logic that appears in the electricity mix, in the health system and in the national care system: make good use of what you have, document it, and build public policy on top of that.
The full map of the country is in Map of the regions of Uruguay, and the costs in Cost of living in Uruguay in 2026. For anyone assessing the country at this stage of life, the picture is in Growing old in Uruguay and in Healthcare in Uruguay.
And when the chosen region turns into a plan to move, that is the path we walk alongside the family in Relocation and Living.
Informational content. It does not constitute medical, real estate, legal or investment advice. Data verified on 21 August 2026 with Uruguayan scientific and official sources. The properties of the thermal waters described correspond to chemical characterisation and classification by analogy, not to clinical proof. Each situation is analysed individually.