Southeastern Anatolia region’s prominent Siirt, standing out with its rich natural resources and cultural heritage, is also a province attracting attention with its geothermal potential. One of the most important examples of this potential is Biloris Thermal Springs, located within the boundaries of Eruh district. Located This thermal spring, also known as “Sağlarca Thermal Springs” among the local people, is situated in a natural cave on the banks of the Botan River. With its mineral-rich waters, geological structure, and health effects, Biloris Thermal Springs is of considerable value and quality, both scientifically and touristically.

Geographical Location and Access

Biloris Thermal Springs is located within the boundaries of Sağlarca Village, affiliated with Eruh district, on the Siirt-Eruh highway, 15-17 kilometers from the district center. , It is located right on the banks of the Botan River, inside a natural cave. By expanding and organizing the cave, the use of thermal water has become possible. Transportation from Siirt to the springs is provided by service vehicles going towards Eruh; it is approximately 17 kilometers away from Eruh center. Besides the main spring that feeds the spring pool, another thermal spring is located nearby, and its waters directly flow into the Botan River. This geographical location makes the springs both accessible and situated in an area surrounded by natural beauties.

Geological Structure and Geothermal Features

The region where Biloris Thermal Springs is located has a complex geological history and is covered with formations from different periods. The oldest unit observed in the area is the Germav Formation, which dates back to the Upper Cretaceous-Lower Paleocene. This formation consists of an alternation of grey-green shale, marl, sandstone, mudstone, and limestone. Above it lies the Gercüş Formation, which dates back to the Paleocene-Lower Eocene; this unit consists of an alternation of maroon marl, sandstone, and conglomerate, and locally contains limestone bands. Above that, there is the Midyat Formation, dating back to the Eocene; the lower levels of this formation contain marly limestone. Above the Midyat limestones is the Şelmo Formation, dating back to the Upper Miocene; this unit consists of an alternation of sandstone, conglomerate, mudstone, and marl. At the top are Quaternary alluvium units: well-moderately cemented polygenic gravelly old alluvium, unconsolidated sand, clay, and gravel forming recent alluvium, and travertine sediments left by hot water around the springs. The total thickness of this sequence reaches 170 meters.

The geothermal activity in the region is related to tectonic movements. NW-SE trending anticlines, synclines, and faults allow the waters in the area to reach the surface. Young basalt outpourings indicate that the geothermal gradient is above normal at some points. The spring waters reach the surface along these fault lines and consist of five different sources:

• Main Spring Source: Temperature 34.5°C, flow rate 90 l/sec.
• Second Source: Temperature 34.5°C, flow rate 10 l/sec.
• Warm Spring Source: Temperature 33.9°C, flow rate unmeasured.
• Cempir Ilısu Spring: Temperature 30.6°C, flow rate 0.01 l/sec.
• Lif Ilısu Spring: Temperature 33.1°C, flow rate 10 l/sec.

The total flow rate of these sources varies between 172-173 l/sec, and their temperatures range from 30-35°C.

Physical and Chemical Properties

The chemical composition of the spring water consists of chloride, sulfate, bicarbonate, sodium, hydrogen sulfide, and calcium minerals. Its pH is 6.4, showing an acidic character. The temperature range of the water varies between 33–36 °C, and its proximity to body temperature makes it suitable for bathing applications.

Health Effects

The healing waters of Biloris Thermal Springs, when used as a bath cure, can have supportive effects in various health problems. Based on scientific literature and local observations, the spring water has benefits. In the chronic stages of inflammatory rheumatic diseases (rheumatoid arthritis, ankylosing spondylitis etc.), in non-inflammatory joint diseases (osteoarthritis, chronic back pain, etc.), it is applied as a bath cure to relieve pain and improve mobility. It is also used to support the mobilization process of patients in cases of prolonged immobility following orthopedic surgeries and nervous system operations. In selected neurological disorders, such as cerebral palsy, the relaxing and balancing properties of the water contribute to the rehabilitation process. On the other hand, thanks to the minerals contained in the spring water, supportive effects have been observed in some skin diseases and gynecological problems.^【1】 

Tourism Potential and Current Situation

Biloris Thermal Springs has the potential for health tourism thanks to its geographical location and natural surroundings. However, currently, the facility infrastructure is inadequate; there are no modern accommodation units, hygienic pools, and comprehensive health services. Also, the mixing of the waters of the Botan River with the spring sources may negatively affect the water quality.

Future Perspective

Biloris (Sağlarca) Thermal Springs is one of Turkey's important thermal areas with its geothermal resources. Despite its potential in health and tourism, due to infrastructure deficiencies and insufficient promotion, this potential has not yet been fully exploited. With increased scientific studies and infrastructure investments, the springs can become an important center for both the local population and health tourism.