The Jezerka NNR was declared in 1969 on a territory of 136 ha. The reserve lies between the towns of Chomutov and Most in the Ústecký kraj - Ústí nad Labem Region on the valley slopes of the Vesnický potok stream and the southern slopes of Mt. Jezeří in the Krušné hory mountain range at elevations between 342 and 706 metres.
The subject of the protection is the preserved mixed forest growths on the southern slopes of the eastern part of Krušné hory covering the rocky and very steep slopes of Mt. Jezeří. The beech stands here are approximately 250 years old and one of the highest oak communities in the Czech Republic can be found on the summit of Mt. Jezeří.
The steep slopes to the NW of the Krušné hory fault line consist of rocks of the Krušné hory Crystallinicum of late Proterozoic to early Paleozoic age. These are predominantly coarse – grained, two-mica to biotite augengneiss and leafgneiss orthogneisses. A number of geomorphological landforms developed here as a result of frost-weathering of the gneisses.
Beech forests, either of the herb-rich type or with wood-rush are the predominant vegetation type in Jezerka NNR. Smaller areas are covered by acidophilous oak forest, talus and ravine forest. Specially protected plant species which grow in the herb layer here include a rich population of perennial honesty (Lunaria rediviva) as well as the wolfsbane Aconitum lycoctonum, narrow-leaved helleborine (Cephalanthera longifolia) and martagon lily (Lilium martagon). On the forest fringes we can also find St. Bernard’s lily (Anthericum liliago) and spignel (Meum athamanticum).
Strong populations of vertebrates which are bound to the old beech growths live in the NNR. Significant species include the fire salamander (Salamandra salamandra) and the smooth snake (Coronella austriaca). Many bird species inhabit the area and nesting species include the stock dove (Columba oenas), black woodpecker (Dryocopus martius), grey woodpecker (Picus viridis), greater spotted woodpecker (Dendrocopos major), sparrowhawk (Accipiter nisus), red-breasted flycatcher (Ficedula parva) and golden oriole (Oriolus oriolus). Tree-dwelling bat species live in cavities in the old trees.
The invertebrate fauna is also significant and 19 forest mollusc species have been recorded, including the gastropods: the door snail Balea perversa, the “cheese” snail Helicodonta obvoluta and the typical snail Causa holosericea.
A major negative influence on the territory is the presence of a large open-cast brown coal mine which lies 50 metres away from the edge of the NNR. Forestry interests would also like to increase the representation of Norway spruce in the forests in the area.
Regular monitoring of vertebrates and vascular plants in the reserve is currently in progress. A new management plan is being prepared, which states that the priority for nature protection is to leave as much of the forest growths as possible to natural processes (non-intervention).
Several marked tourist trails lead through the NNR. These paths and the neighbouring Jezeří Chateau are visited by large numbers of tourists, especially in the summer season. We are preparing to install larger information panels around the edges of the NNR.
The land in the reserve formerly belonged to the Lobkowicz family estates and this noble family built the Jezeří Chateau on a nearby headland. Commercial forestry was forbidden in the area from the early 20th century but the current owners are not as generous to nature.
A small reservoir with a catchment area of 36 km² lies in the NNR on the Vesnický potok stream.