Lissos, also known as Filiouris, is a river in Thrace. Its springs are located in Megalo Livadi (Vyrsini mountains), near the borders of the regional units of Evros and Rodopi. It flows into the Thracian Sea, near the settlement of Imeros. At this point, the river creates an extensive wetland system that reaches 13 square kilometers. Despite its continuous degradation in recent years, the river has rich flora and fauna.
Many rare species of birds live here, such as - among others - the rare white scavenger vulture, the golden eagle, the rare eastern imperial eagle, the lesser spotted eagle, the short-toed snake eagle, and others. The area is regularly visited by black vultures, griffon vultures, and starlings. Roe deer, wolves, rare jackals, and wildcats live in the forests around the river.