Maritsa/ Evros/Meric River Basin

Bulgaria, Greece and Turkey share the basin of the Maritsa/Evros/ Meric River.

Hydrology and hydrogeology

The Maritsa/Evros/Meric River is about 500 km long, has its source in the Rila Mountain (Bulgaria) and flows into the Aegean Sea. Major transboundary tributaries include the rivers Arda/Ardas  (Bulgaria, Greece and Turkey), Tundzha/Tundja/Tunca (Bulgaria, Turkey) and Biala/Erithropotamos (Bulgaria, Greece). The river Ergene is an important tributary, located in Turkey.

The basin has a mountainous character at its upper part; low mountains and plains cover the major part of the basin. The average elevation is 100 m a.s.l.

The climatic and geomorphologic characteristics of the basin lead to specific run-off conditions, characterized among others by high inter-annual flow variability. Floods in all three sub-basins may cause severe damage in all three countries; among the most disastrous were the floods in 2005 (recurrence interval, 1,000 years), 2006, and November 2007.

Bulgaria reported that climate change has affected the basin over the last 20 years, resulting in an approximately 30% decrease in precipitation, and a subsequent decrease in water resources.

Turkey reports that the Evros/Meric is a transboundary alluvial aquifer between Turkey and Greece. It drains through the Meric/Evros River that forms the border between Turkey and Greece. It is mainly used for irrigation, industry, and drinking water purposes in Turkey.

Topolovgrad Massif, shared by Bulgaria and Turkey, is a karstic aquifer, with medium connections to surface waters of Tundzha/Tundja River sub-basin (see aquifer table under Tundzha/ Tundja River). Cooperation is necessary among the three countries to delineate the boundaries of the transboundary aquifers in the basin and enhance relevant knowledge. Moreover, Bulgaria suggests that the countries should cooperate to clarify the stratigraphy of the Orestiada/Svilengrad-Stambolo/Edirne and Evros/Meric aquifers. As reported, due to the Paleogene aquifer in Svilengrad and Ivailovgrad, it is possible that Evros/ Meric extends also in the territory of Bulgaria.

Pressures, status and transboundary impacts

The delta of the Maritsa/Evros/Meric River, shared by Greece and Turkey (150 out of the 188 km2 of the delta lies in the Greek territory), is of major ecological significance. It is one of the most important wintering areas for birds in the Mediterranean. A major part of the delta in Greece (100 km2) has been designated as a Ramsar Site; it also enjoys the status of Special Protected Area and Natura 2000 site. Some 33% of the Bulgarian part of the basin has been also designated as Natura 2000 sites. Areas of ecological importance in Turkey are under national protection status. Areas near the delta are used as agricultural land.

The total number of reservoirs in the Bulgarian part is as high as 722. Hydropower production is common in the upper part of the basin, and cascades of dams form big reservoirs. Many small dams are used for irrigation purposes and fish-breeding. In Turkey, seven dams and one regulator are under operation on the Ergene River and its tributaries, serving irrigation, flood control and some drinking water supply purposes (15% of drinking water of Edirne and Kırklareli cities is supplied from two reservoirs, Suloglu and Armagan). There are also 53 small dams located on several tributaries used for irrigation. In Greece a number of dams are used for irrigation purposes.

Depending on climatic conditions and needs, the operation of the dams upstream has a share in the variability of flow. Reduced flows, when they occur, may lead to saltwater intrusion.

In Bulgaria, the operation of small hydropower stations and gravel extraction have led to hydromorphological changes in the Maritsa, Arda and Tundzha Rivers. Abstraction of groundwater for irrigation and partly for industrial use (textile, food, paper, cement production) in Turkey has led to a decline of piezometric levels by 10-12 m since the 1990s; as a response measure, groundwater abstraction in the Ergene sub-basin has been forbidden.

In Bulgaria, untreated urban wastewater is a source of pollution; wastewater collection facilities serve 67% of the population, while 30% of wastewaters in the Maritsa sub-basin are treated. Construction of collection and treatment systems is ongoing. By magnitude, diffuse sources are the second biggest pressure; 74% of diffuse pollution comes from agriculture. Nitrate pollution in groundwater is one of the effects. Industrial activities in the Bulgarian part (including food production and production of non-ferrous metals and chemicals) may be a potential source of heavy metals, as well as of organic and nitrogen pollution of local importance. Mining activities in mountainous areas are sources of surface and groundwater as well as sediment pollution; impacts on ecosystems are also possible. Officially-registered regional waste disposal sites are gradually replacing the old ones in Bulgaria: in the river basins of the Maritsa, the Arda and the Struma, there are already six in operation.

Untreated domestic wastewater is one of the main pollution sources also in Turkey, particularly in the Ergene sub-basin; the river is Class IV (very polluted water), threatening human health and biodiversity. Both urban wastewater and solid waste volumes have increased due to population growth. The construction of wastewater treatment plants for municipalities in the basin is expected to improve the situation; these are planned to be completed by 2012. Illegal waste disposal is also a pressure factor; pollution of water from controlled disposal areas was also reported. Industrial development since 1980 has led to the increase of the concentration of related pollutants e.g. in Ergene River; this is linked with illegal wastewater discharges. Unsustainable agricultural practices are an additional pressure factor; these are related to the use of fertilizers and pesticides (resulting in nitrogen, phosphorus, and pesticides pollution), and inefficient irrigation techniques. Groundwater pollution is the outcome of the aforementioned pressures. Turkey reports that there is loss of biodiversity in parts of the basin.

According to Turkish assessments, the water quality status of the Meric River is Class III (polluted water), both at the point where it enters the territories of Turkey, and at its mouth at the Aegean Sea. The Tunca is reported as Class IV (very polluted water) with regard to heavy metals at the point entering Turkey.

Transboundary cooperation

Existing bilateral agreements and cooperation in the basin cover issues of flood protection (in the river Tundzha/Tundja/Tunca) and joint infrastructure projects, as well as general environmental cooperation, including conservation of protected areas. A reference should be made to the 1975 and 1993 agreements between Bulgaria and Turkey; the 1964 and 1971 agreements between Bulgaria and Greece; and the 1934 agreement between Greece and Turkey. There is communication between Bulgaria and Turkey regarding the possible construction of the Suakacagi dam on the Tundzha/Tundja/Tunca River at the border between the two countries, aiming to address issues related to flooding. The major part of the construction would extend to the Bulgarian territory.

Building on the existing bilateral cooperation arrangements, the establishment of a cooperation mechanism in the whole basin, involving all three riparian countries, should be considered. Initiatives that touch upon transboundary concerns e.g. ecosystems and biodiversity, may provide the enabling environment for the initiation of a dialogue. The ongoing cooperation process between Bulgaria and Turkey to limit and prevent the damaging effects of floods provides an additional “entry point” for the enhancement of cooperation; Greece should be included where appropriate. A coordination structure including the experts of three riparian countries may be considered as an initial step.


In Bulgaria, the monitoring network includes 27 stations for surveillance monitoring, and 48 for operative monitoring (quality monitoring is performed). Hydrological parameters are planned to be monitored in 25 stations. In Turkey, monitoring of water quality is carried out periodically at five monitoring stations on the Meric, one on the Arda, and one on the Tunca, since 1979. Cooperation between the competent authorities of Bulgaria and Turkey has led to the establishment of four telemetry hydrometric stations in the Bulgarian part (one on each of the Arda and Tundzha/Tundja/Tunca Rivers and two on the Maritsa/Meric River) that supply real-time data.

Bulgaria is working to update hydrological data, mapping the sensitive areas, and creating a hazard map. As the downstream countries, Turkey and Greece, are highly vulnerable to floods, it is evident that measures for flood prevention can only be improved, and their effects be mitigated through cooperation and use of common information sources. Joint development and establishment of integrated information systems such as flood forecasting/early warning systems is essential. The cooperation between Bulgaria and Turkey in this regard provides a basis for further action. The broadening of the scope of related activities in the future to also include Greece is deemed necessary. The use of better dam operation techniques and rules can considerably mitigate floods.

The operation of the dams should be carried out in a coordinated manner among the riparian countries, in accordance to upstream downstream needs and considerations; the need to preserve the natural values of the delta area should also be taken into account. The implementation of good agricultural practices and the establishment of buffer zones are response measures taken in Bulgaria to address diffuse pollution from agriculture. There is a need to restore the existing irrigation infrastructure.

In Turkey, the development plans for the Meric-Ergene Basin integrate up to a point the development strategies in waterrelated sectors. There is no conjunctive management of surface water and groundwater. The Protection Action Plan for Meric- Ergene Basin (2008) assesses the effects of development projects and economic activities on the environment, and provides for a short, medium and long-term action plan in terms of water resource management. There is also a land use plan for the Meric-Ergene basin.

The respective parts of the Maritsa/Evros basin are within the East Aegean Basin District in Bulgaria and the Eastern Macedonia and Thrace District in Greece; there is a management authority and a basin council in each of these Basin Districts.

An RBMP for the East Aegean Basin District (Bulgaria) was finalized with the involvement of stakeholders. Water demand management measures in Bulgaria include water abstraction control.


1 The river is called Maritsa in Bulgaria, Evros in Greece and Meriç in Turkey.

2 The river is called Arda in Bulgaria and Turkey, and Ardas in Greece.

3 The river is called Tundzha and/or Tundja in Bulgaria and Tunca in Turkey.

4 The river is called Biala in Bulgaria and Erithropotamos in Greece.

5 Measures to improve hydrologic conditions (e.g. forestation), reduce water loses and increase water use efficiency are included in the program of measures of the River Basin Management Plan in Bulgaria; the programme specifically refers to studies to investigate the impact of the climate changes as necessary. No detailed information has been provided by Bulgaria on the spatial or temporal extent of the underlying observations.

6 Big water cascades on Maritsa include: Cascade Vacha (2 dams with 5 hydropower stations), Cascade Batak (5 dams with 3 hydropower stations), and Cascade Belmeken-Sestrimo (1 dam reservoir with 4 hydropower stations).

7 These include those on the rivers Ardas, Lyra, Provatonas, Ardanio and Komara (when last reported in the First Assessment, the last was under construction).

8 PHARE Technical Assistance for Flood Forecasting and Early Warning System – project on “Capacity Improvement for Flood Forecasting in the Bulgaria-Turkey Cross-Border Cooperation”.

Aquifers in the Maritsa/ Evros/Meric River Basin

Orestiada /Svilengrad -Stambolo/Edirne Aquifer - 143