Evros River, the natural border between Greece and Bulgaria and Turkey, has a total length of 530km. of which 230km. belong to Greece. It is the second largest river in the Balkans after the Danube, Evros stems from the Rila Mountains in Bulgaria and flows into the Thracian Sea, irrigating its way across the plain of the prefecture. Evros is characterized by remarkable fish and riparian thickets of great ecological value, while the proximity of the water system of the river with the mountains of Rhodope created great variety of habitats with rich fauna and flora. The navigation of small vessels is possible until the height of Adrianoupoli. Tributaries of Evros in Greece is the Arda River, which crosses the Triangle area to the north of the county, the Erythropotamos, which passes through the hilly and lowland Metaxades-Palouri and crosses the city Didymoteicho as well Diavolorema, the Kamilopotamos and the Grand Stream. The river is characterized by large volumes of water and sediment transported to the estuary. The habitats of the area are of exceptional interest, like the flora with 350 recorded plant species. The four lagoons and salt steppes present in the Evro"s delta habitats are a European priority. The area is characterized by the presence of 6 important plant species. Among these, water chestnuts (Trapa natans) is included in the lists of the World Conservation Monitoring Centre and Nature (WCMC) and the European Red List of Endangered World Animals and Plants (European Red List Data of Globally Threatened Animals and Plants, a kind of (Iris spuria ssp. ochroleuca) is protected by Presidential Decree 67 (FEK 23/A/1981), 3 species (Cenchrus incertus, Heliotropium curassavicum, Leymus racemosus ssp. sabulosus) are rare in Greece and the region of Northern Greece constitutes the extreme limit of their spread and one species (the sea lily - Pancratium maritimum) is threatened by human activities on the coast.