Lake Mir is located in the southwestern part of Nature Park Telašćica. The lake is located in a narrow strip of land between Telašćica Bay and the open sea. After the last ice Age, the global sea level rose by approximately 120 metres, and the karst depression was filled by sea water through numerous underground microcracks, especially numerous on the northern side. The sea sources can easily be noticed at high tide. The lake is about 900 m long, and its greatest width is about 300 m. The greatest depth is 6 m. The lake is salty due to underground connections to the sea. The salinity of the lake is generally higher than the salinity of the surrounding sea due to evaporation and enclosedness. Very small water level changes have been noted because of the small permeability of the cracks connecting the lake to the sea. During stormy jugo wind, the sea spills over into the lake in its southeastern part. The lake shore is mostly low and rocky, with numerous limestone rocks, and only in the extreme southwestern part a lesser accumulation of sand can be observed. The bottom of the lake is rocky in the shallow parts, and covered in pelitic bottom deposits in the deeper ones, with fango (healing one) in one part.

Temperature fluctuations in the lake are very prominent (in summer to 33°C, in winter to 5°C), therefore the lake is warmer than the sea in summer, and colder in winter due to its shallowness. The salinity of the lake is above average due to evaporation. These extreme conditions are the reason for the biological poverty of the lake. In addition to the plankton, there are only a few species of marine organisms in the lake. These are: algae, goby, mullet, sea bass, several species of shellfish, see snails, crabs, and a special type of eel that grows up to 3 kg.