Ohrid Lake

Ohrid Lake

Lake Ohrid is one of the few ancient lakes in the world that provide continuous freshwater habitat for more than 1 million years, and the only one in Europe.

Lake Ohrid (altitude: 695 m) is oligotrophic, deep (maximum depth 289 m; average depth 164 m), large (area 358 km2) and one of the most voluminous lakes (~ 55 km3) in Europe.

The water balance is dominated by the inflow from karst aquifers (~ 50%) with smaller shares of inflows and direct rainfall (Matzinger et al., 2006) [Matzinger A, Z. Spirkovski, S. Patceva, A. Wüest. Sensitivity of ancient Lake Ohrid to local anthropogenic impacts and global warming. J Great Lakes Res., 2006; 32: 158–179]. Evaporation (40%) and the main outflow, the Crn Drim River (60%) balance the water budget of Lake Ohrid.

Lake Ohrid is characterized by exceptional biodiversity, taking into account even the microscopic algae. As with other living organisms, the Lake is characterized by the presence of rare and tertiary relict species of algae. Diatoms (Bacillariophyceae) appear to be an important group of microscopic algae, followed by green algae (Chlorophyceae). A total of 789 diatom taxa have been registered in Lake Ohrid, of which 117 (14%) are considered endemic to the lake and 15 (about 2%) are considered relict species, or previously known only from fossil deposits in Romania (Levkov and Williams, 2012). The number of species registered for Lake Ohrid continues to increase. Most lake species can be considered characteristic only of very clean waters with fairly low concentrations of nutrients, especially nitrogen and phosphorus (Miho et al., 2004).

The macrophytic flora in the shore of Lake Ohrid can be divided into different belts: chara species at a depth between 3 and 30 m, different species of submerged plants and a discontinuous belt of reeds (Phragmites australis) along the shore (Albrecht and Wilke, 2008) [, 5 Albrecht C., T. Wilke. Ancient Lake Ohrid: biodiversity and evolution. Hydrobiology, 2008; 615: 103–140]. The reed belt is a particularly important habitat for many other organisms, including fish, frogs, and waterfowl.

There are extremely rich and diverse representatives of the fauna in Lake Ohrid, most of them endemic. 586 benthic macroinvertebrates have been recorded in the Lake, with endemicity levels ranging from 50 to 90% for certain benthic groups (flatworms, oligochaetes, leeches, isopods, amphibians, etc.), a fact that gives the lake the seal of an aquatic ecosystem. the highest percentage of endemic species per square meter in the world.

The rich and unique fauna of Lake Ohrid includes various types of relict forms such as the Ohrid round sponge (Ohridaspongia rotunda) or the very small endemic snail (Gocea ohridana). In general, the richest, most diverse and with the highest endemism is the group of freshwater snails (Gastropoda) among which the level of endemism reaches 86% of the 72 registered species.

According to the IUCN assessment of the representatives of the benthic fauna registered in Lake Ohrid, 28 species are assessed as vulnerable, 17 as endangered and 10 as critically endangered, a fact that