Morské oko lake and the nearby Sninský kameň peak are gems of the Vihorlat mountain range. The natural lake Morské oko, also called ‚Great Vihorlat Lake‘, ranks among the most beautiful natural places of Eastern Slovakia. It is situated in beech forests of the Vihorlat mountains, in the protected landscape area Východné Karpaty (Eastern Carpathians).

Creation of the lake dates back to the final period of volcanic activity in Vihorlat. A massive landslide from the eastern slopes of Montrogon and Jedlinka peaks enclosed the Okna brook valley and thus this most famous natural lake in Vihorlat came to an existence. The lake has 6-8 permanent and occasional springs and excess water flows to the Okna brook through the barrage of the dam built in 1880s.

The evolution of the lake continues even today. Natural processes and human activity (forest roads building, wood processing) increase erosion. Consequently, more soil and mould gets into the lake through its tributaries, which causes gradual clogging and speeds up the natural process of lake ageing. Apart from soil and mould it is also organic material (leaves, branches, bark, etc) that gets into the lake; it decays in water and thus depletes water of oxygen. Water then contains more nutrients, which enhances growth of water grass and the water becomes opaque. To reduce or stop inflow of muddy water with leaves and other impurities into the lake, small dams were built on the main tributaries.

Attempts to protect Morské oko date back to the 1950s. In 1949 the Morské oko lake features in the proposal for the reservations network. To protect natural values, the lake and surrounding forests were proclaimed the national nature reserve with the fifth level of protection in 1984. The total area of the reserve is 108,48 hectares.

This picturesque mountain lake (618 m above sea level) has a shape of an irregular pentagram when looked at from the Sninský kameň peak (1005 m above sea level). Its width is 312 m, length 775 m and depth reaches 25-28 m. With the total area of 13 hectares it is the largest volcanic lake in Slovakia. The water level changes during a year. The difference between the highest level in spring and the lowest level in autumn can be as much as 3 m, depending on the annual rainfall.

Each year many tourists visit the Morské oko lake, coming to explore this lake, unique in Europe due to its rich flora and fauna. The most frequent are beech forests, often with remains of primeval forest. From coniferous trees the only original species in this locality is fir. As for plants, the most widespread are Doronicum austriacum, Dentaria glandulosa, Mercurialis perenis, Prenantes purpurea, Scopolia carniolica and Sedum carpaticum.

The Morské oko lake is interesting not only for its creation, location and beauty, but also thanks to its mysterious underwater life. Originally, only three species of fish lived in the lake - Salmo trutta m. fario, Barbatula barbatula and Phoxinus phoxinus. At present there are 13 kinds of fish to be found in the lake and its tributaries, the most dominant of which is the European chub (Leuciscus cephalus).

Amphibians found so far in the area were: Fire Salamander (Salamandra salamandra), Common Toad (Bufo bufo) and Common Frog (Rana temporaria). Typical reptile species in the area are Elaphne longissima and Viperia berus. In the surroundings it is possible to spot a deer, fox, pine marten; occasionally grey wolf and lynx. The Eurasian otter (Lutra lutra) was seen near the Morské oko lake. As for birds in the area, very interesting are: Ural Owl (Strix uralensis), Black Stork (Ciconia nigra), Black Woodpecker (Dryocopus martius), White-backed Woodpecker (Dendrocopos leucotos), Grey wagtail (Motacilla cinerea) and other.

The Morské oko lake is a state nature reserve with protected flora and fauna, therefore fishing, rowing and swimming are strictly forbidden!

To the west from the Morské oko lake, a Malé (small) morské oko lake is located. From the point of evolution, Malé morské oko is older. It is situated 727 m above sea level, it covers the area of 0,32 hectares and its maximum depth is 3 – 3.5 m, depending on rainfall and spring strength.

At present the Malé morské oko lake is a nature monument with the fifth level of protection.

The area of the PLA Vihorlat is situated in the easternmost part of Slovakia. On the north, the Vihorlat mountains are separated from the Bukovské mountains and the Laborec mountain range by the Beskidian Piedmont. On the west and south they border with the Eastern Slovak Hills (Východoslovenská pahorkatina). The PLA area has an irregular shape. It covers the middle part of the Vihorlat mountain range. The lowest PLA point is the edge of the forest next to the village of Remetské Hámre (320 m), the highest is the hill Nežabec (1023 m). Administratively, the area is divided between counties Michalovce and Humenné. It spreads across the counties of Michalovce, Sobrance, Humenné and Snina. It reaches into cadastral areas of the villages of Jovsa, Poruba pod Vihorlatom, Remetské Hámre, Hlivištia, Choňkovce, Podhoroď, Ruská Bystrá, Vyšná Rybnica, Stakčín, Snina, Zemplínske Hámre and Valaškovce.

Vihorlat was proclaimed a PLA on December 28, 1973, according to Act SNR no. 1/1955 of the Statute, by the edict no. 9 MK SSR, in order to protect and develop nature and natural resources, provide coordination of its economic usage in concordance with the natural resources and natural beauties protection, bearing in mind their universal cultural, scientific, economical and recreational importance. This PLA has the second level of protection. One of the main tasks resulting from the PLA mission is to build a representative network of small protected areas and thus securing protection of the most valuable parts of nature in the form of nature reserves, protected areas and nature monuments.

Thanks to its size, the protected landscape area Vihorlat ranks among our smallest large protected areas. The total area of the PLA Vihorlat is 4 383 hectares, protective zone 25 350 hectares. Volcanic activity created a number of small lakes, which later changed into moors and mosses.

Even despite its small area and altitude, Vihorlat is an impressive mountain range. It spreads over large East Slovak Lowlands and its highest peaks outreach 1000 meters. Its geographical location and distinctive geological evolution caused the creation of such natural curiosities as the Morské oko lake, the Sninský kameň peak, highland mosses or cohabiting of species of plants from western-Carpathian, eastern-Carpathian and Pannonian flora. Geologically, most of the area belongs to neovolcanites of the Vihorlat mountains. Crater parts of the ancient volcano can be found in the area of the Morské oko lake and of Porubský brook. Typical for the area are mainly andesites and their equivalents.

The following smaller nature reserves with various levels of protection belong to the PLA:

• National nature reserve Morské oko (1984)
• National nature reserve Vihorlat (1986)
• National nature reserve Jovsianska hrabina (1953)
• Nature reserve Jedlinka (1988)
• Nature reserve Machnatý vrch (1988)
• Nature monument Čierny potok (1988)
• Nature monument Malé Morské oko (1992)
• Nature reserve Lysák (1993)
• Nature reserve Lysá (1993)
• Nature reserve Drieň (1993)
• Nature reserve Baba (1999)
• Nature reserve Pod Trstím (1993)
• Nature monument Beňatinský travertín (1989)
• Nature monument Hradný vrch Podhoroď

PLA Vihorlat is of great importance for tourism and its development. The area enables visitors to get to know natural beauty and natural resources of this part of the country. From the point of view of tourism, the most famous and frequently visited localities of the protected landscape area are the National nature reserve Morské oko and the lake with the same name, which, due to its appearance and its origins, represents a gem not only of this PLA, but also within Slovakia in general. Above the lake, on the north, another PLA dominant point towers – a protected natural creation the Sninský kameň peak (1005 m), which offers a panoramatic view of its northern and southern sides. It is worth exploring mainly due to its rich fauna and flora. On its southern side a variety of exothermic species of flora can be found; the northern part shows flora of mountain beech forests. In the northern part of the PLA, not far from the town of Snina, are located Sninské rybníky lakes, which form a recreational centre with swimming, relax and sport facilities.

Overall, there are 88 km of maintained tourist trails in the PLA. The main dominant features are the Vihorlat mount (1075 m above sea level), Sninský kameň peak a Morské oko lake. For walking and cycling the PLA visitors can use the educational trail Morské oko - Sninský kameň - Sninské rybníky, open in 1984. The trail features information panels, providing facts about history and other peculiarities of this protected landscape area.

PLA Vihorlat belongs to the most densely forested mountain ranges in Slovakia, with majority of foliaceous, especially beech forests. It is situated on the border of Western and Easter Carpathians and along the border of Carpathian and Pannonian flora, which is visible in the wide variety of flora in the area. The most frequent are beech forests, often with remains of primeval forest. In lower parts also oak and oak-hornbeam forests can be found. The original coniferous species are precious, only in the area of Morské oko visitors can see spruces and firs. Typical for the area are Doronicum austriacum, Cicerbita alpina, Salix silesiaca, Gentiana asclepiadea, Homogyne alpina, Lycopodium sellago, Cyanus montana ssp. Mollis, Polygonatum verticillatum, Telekia speciosa, Scopolia carniolica, Symphytum cordatum or Aposeris foetida. The very rare Sedum annuum, typical for the Low Beskydy mountains and Slovenské Rudohorie, can be found on Sninský kameň. In total, there are 35 species of protected plants in the PLA.

Influence of the East Slovak Lowlands and Eastern Carpathians is visible in the composition of the fauna of Vihorlat. There is more than 2000 species of invertebrate. Among vertebrate found in the area, very characteristic are e.g. Carpathian newt or Aesculapian snake, as well as almost 100 species of nesting birds, e.g. Black Stork, Honey Buzzard, Lesser Spotted Eagle or Short-toed Eagle. Higher areas are inhabited by elks, the lower ones by roe deers. An Eurasian lynx or wild cat can be seen, more often a badger, Pine marten or Beech marten, Occasionally, a Eurasian otter can be found and also wolf tracks can surprise the Vihorlat mountains visitors. Brown bear is also a rare view. Beech forests of Vihorlat are a home of rare beetle Rosalia longicorn.

Rivers in the whole area empty into the Black sea, the river Tisa, with the river Bodrog network, draining the whole area. The north-eastern part of the PLA Vihorlat is drained by the Cirocha river, with basin area of 500 km2, which empties into the Laborec river after 50,6 km, close to the town of Humené. From the eastern slopes of Vihorlat flow major streams, e.g. Luh, Savkov brook, Strihovský brook and other. In the central part, the network of rivers consists of the Okna stream with its tributaries Skalný brook, Ceremosna, Barlahov brook, Lysaka and Rybnička. An important place in the complex of the volcanic mountain rang Vihorlat belongs to the lakes. They represent a unique example of evolution and gradual disappearance of lakes. The largest lake is the Veľké Vihorlatské lake, also called Morské oko. To the north of this lake lies the Malé Vihorlatské lake (727 m above sea level), also called Malé morské oko. The lake has a changing level of water, depth of the lake varying from 2.5 m to 4 m. The lake’s spring was partly blocked during the incline building. One of the peculiarities of the lake is that it has no surface drain, even though it has a constatnt inflow of water. Other lakes are located to the north of the Motrogon hill. The most significant of them being the lake Kotlík (850 m above sea level) with area of 3 - 3,4 hectares, the depth varying from 0,5 to 2 m. This lake is significant mauinly due to a rich newts’ occurrence. Other lakes are situated in the northern part of the PLA and are in various stages of disappearance. The most significant of these lakes is the disappearing lake Podstavka (1,6 hectares), surrounded by andesite slopes. The maximum depth of the original lake was 21 m. Another vanishing lake is the mossy lake Hypkania (2,3 hectares), the original depth of which was 10,8 m. Evolutionally youngest moss type is the Ďurova mláka pond. Apart from the abovementioned lakes, there is a great number of other lakes, the edges of which are hardly recognisable and the process of their vanishing can be seen as completed.

This unusual flora and fauna of the Vihorlat beech forests will undoubtedly catch interest of any visitor. Tourists can admire natural beauty all around them. Silent forests of the Vihorlat mountains, mysterious rustle of trees around Morského oko, a sight of blue forget-me-not or dominant rocks of the Sninský kameň peak and a circling eagle above this endless woodland – all that is just a beginning of natural beauty in this spectacular part of the protected landscape area Vihorlat.