Lake Ohrid, that came into being between four to ten million years ago, is Europe's oldest lake, and is amongst the oldest in the world. It is a typical oligotrophic lake, meaning that it contains low levels of nutrients. By its origin the lake is a tectonic one and belongs to the so-called group of "Dasaretian lakes" (named by an ancient region called Dasaretia). The Lake came about in the tertiary period, prior to the glaciation.
Otherwise, most of the lakes of the world came into being immediately after the end of the latest glaciation period. Only a few lakes in the world are older than this one. Famous examples are Lake Baikal, Caspian Lake, and Lake Tanganyka and just a few lakes situated on Celebes, Philippines and China.
Research on the living world of the Lake Ohrid has shown the existence of an exquisit flora and fauna, prolific in endemic, as well as relic fauna forms. Thus, the Lake is thought to be unique in Europe. Similarities can be found only with Lake Baikal and with the Caspian Lake.
Lake Ohrid lies in the valley between Ohrid and Struga, in the border region between Macedonia and Albania. It is situated on 41 degree northern latitude and 20 - 21 degrees eastern longitude, and its altitude is 695 metres above sea level. It covers an area of 358.2 square kilometres, two thirds of which belong to the Republic of Macedonia, and the rest to the Republic of Albania. The shoreline is 87.5 kilometres long - the maximum length being 30.8 kilometres, and its maximum of 14.8 kilometres. The average depth is 164 metres, and the maximum depth 289 metres. The Lake is sorrounded by mountain ranges of Mount Mokra (Mokra Planina - 1589 m.) and Jablanica (1945 m) on the Albanian side and by the limestone ridge of Mount Galicica (2255m) on the eastern side.The surrounding mountains are extremely karstic.
Lake Ohrid is the seventh deepest lake in Europe.
Most of the Lake's water bulk comes from numerous surface and underground springs. That is the reason certain researchers consider it unique in the world. Most of the surface springs lie along the southern shore, near the monastery of St. Naum on the Macedonian side, and near the villages of Tusemiste and Starovo and the town of Pogradec in Albania. There are about 40 rivers and springs that flow into the Lake (23 on Albanian, and 17 on Macedonian territory). During summer, most of them dry out, whereas the rivers Sateska, Koselska, and Corava are the only waters with sighificant waterflow that feed up the Lake.
In the beginning of this century J. Cvijic stated his assumption that the water of the adjacent Lake Prespa, with a water level 158 metres higher, will sink through the karstic areas of the mountains Galicica and Suva Gora. By using natural isotopes, in 1980 it was proved that the lakes of Prespa and Ohrid were connected hydrographically. Evidence have confirmed that more than 50% of the water from the springs near St. Naum come from the Lake of Prespa.
The climate of the Lake Ohrid is classified as a local-continental type. Medium annual temperatures average to 11.4 degrees Centigrade. Medium monthly temperatures average to about 21.2 degrees in July and August, and 34.4 being the absolute maximum in August. The lowest medium monthly temperature amounts to 1.5 degrees in January, whereas - 17.2 degrees is the absolute minimum. The average annual rainfall in the Lake basin amount to approximately 759 mm.
The most common wind is the one blowing from north, particularly in autumn and winter. The winds blowing from southern and south-east directions dominate during spring and summer periods. Southeast and east winds are insignificant. Windy and calm periods change during the day, particularly in summer. Mornings are characterized by the shifts between blowing northern winds and calm periods. Weather conditions become quite different in the afternoons when the southern and south-east winds overtake the silence. Average speed of the wind in the Ohrid region is relatively low, 3.4 m/sec.
The water temperature in the deepest layers of Lake Ohrid is approximately 6 degrees Centigrade, whereas the surface layers may warm up to 24 degrees, and even to 26 degrees closer to the shore.