Lake Doiran straddles the border of Greece and FYROM, being a relic of the large ancient lake Paionia. It covers an area of 43.1 km² (16.6 sq mi) shared between FYROM (27.3 km², 10.5 sq mi) and Greece (15.8 km², 6.1 sq mi). To the west is the city of Nov Dojran, to the east the village of Mouries, to the north the mountain Beles and to the south the Greek town of Doirani. It has a rounded shape and a maximum depth of 4 meters. The lake is a significant natural asset and a valuable resource for communities around the lake.
Due to the overuse of the lake's water for agricultural purposes, within the period 1988-2002, the Doiran Lake water level decreased seriously (6 m) and the littoral zone of the lake became dry. This water level decline together with the simultaneous water quality deterioration resulted in a biodiversity diminish and plankton reduction. The disaster was avoided after both countries took measures to replenish and sustain water levels. Frequent and heavy rainfall in later years helped significantly the lake to keep its water level.
The variety of ichthyofauna makes the reservoir lake attractive not only for permanent inhabitants, but also for migratory birds. Its fauna includes both invertebrates (protozoa, or one-celled organisms, sponges, worms, molluscs, arthropods and insects), and vertebrates (fish, amphibians, reptiles, birds and mammals). Twelve endemic fauna species have been registered in the lake, including the cormorants and the Dalmatian pelicans, listed in the number of vulnerable species on the IUCN list. Due to this fact, Lake Doiran is a significant wetland in Northern Greece. It also hosts a large population of assorted herons, snipes, avocets, ducks, and diving ducks. In the Doiran there are 16 species of fish including carps, perches, pikes, and roaches.
The coastal area of the reservoir in some areas is densely overgrown with reeds. Oaks, alders, and unusual plane trees are set in 590 acres of the coastal area. That area is a stopover for many species of migratory birds. "Mouria Forest", also known as "Forest of thousands of trees", is considered a natural monument and has been nominated for entry into the list of protected areas of the European Union "Natura 2000".
Lake Doiran is the place where the Battle of Doiran took place in 1913 between the Greek and the Bulgarian army. The lake was also on the southern line of the Macedonian front during World War I, and its southern shore became the site of the various battles between allied troops and Bulgarian troops in 1916, 1917 and 1918. Two cemeteries for Greek and British troops stand on a hill a few hundred meters south of the lake.