Lake Ohrid represents a refugial ecosystem which harbors a great number of endemic and relics living forms. Though the whole Lake's fauna characterizes high biodiversity and endemism, this is most obvious in the class of Gastropoda. Unlike the Lake, the fauna of the adjacent waters fairly differs from the Lake's fauna, i.e., it is poorer both in term of diversity and endemism. The main goal of our study was to perform comparative biocenological researches on the gastropod fauna from Lake Ohrid and the adjacent waters in the watershed of the Lake. Based on the results we have obtained, it could be clearly noted that different habitats are characterized with different qualitative composition of the gastropod fauna not only when compared the gastropod settlement between the Lake and its surrounding waters, but also in the Lake for itself. Total of 50 species of gastropods have been recorded in the littoral regions of the lake and its coastal waters during 2009/2010. They belong to subclass Orthogastropoda (50 taxa). 21 species out of 50 are recorded in the adjacent waters: 13 of them settle both the adjacent waters and the Lake, while 8 strictly inhabit the adjacent waters. In terms of endemism, 17 are endemic and 4 cosmopolitan. The remainig 29 (out of 50 recorded) settle up only the littoral zone of the Lake: 25 are endemic and 4 are cosmopolitan. The percentage of endemism based on the recorded species for the class Gastropoda is 84%.

Lake Ohrid is the oldest and deepest lake on the Balkan Peninsula and one of the five oldest lakes in the world. Two of the most striking attributes of the species of the Lake’s fauna, especially the fauna of gastropods, are the high level of biological diversity as well as a high percentage of endemism. The main subject of interest in our research was to follow the distribution and density of the endemic gastropod species Chilopyrgula sturanyi. For this purpose different depth points of the transect Hydrobiological Institute-Radozda as well as other littoral points on the northwestern part of Lake Ohrid, were investigated. The results showed maximum density in the population of Chilopyrgula sturanyi in the muddy lakebed covered by Chara tomentosa. The minimum density in population was recorded on the lakebed with gravel. Specimens of Chilopyrgula sturanyi were not recorded at the depth of 50 m, where the lakebed is covered by a sandy-muddy substrate

Our research into 52 profiles of the littoral zone of the Macedonian part of Lake Ohrid and numerous samples taken from its surroundings has resulted in a detailed picture of the composition of the Charophyta vegetation in the lake. The results of the research also include data regarding the species composition and present state of Nitella. The dominant species of Nitella is Nitella opaca, which is characterized by a specific distribution, morphological variability and ecology. The present state of Nitella is not steady, especially in the watershed of the lake, since in this area there are some permanent changes in the hydrology of the terrain. Therefore, there is a need to establish long-term and complex monitoring which will result in the prompt detection of risk factors and influences, thereby enabling a rapid reaction to a possible newly emerged negative state