The Rupel Gorge or Rupel Pass (Greek: Στενωπό του Ρούπελ; Bulgarian: Рупелски пролом) is a steep river valley in the northern part of Central Macedonia, immediately after the Greek-Bulgarian border.[1] It was formed by the Strymon River, which stems from the Vitosha mountains and flows into the Aegean Sea. The gorge is rich in biodiversity which may be endangered by the project to build the Motorway 3 which is a part of European route E79. Strymon enters from Bulgaria into Greece west of village Promachonas, going through Roupel Pass, that it opened up, between the mountains Belasica and Orvilos. To this point, cause of a rough change of incline of the ground, Strymon looses his dash and splits into two branches. The west branch goes to lake Kerkini and then flows southeast where he joins again the east branch near to village Lithotopi.