Lake Ohrid ( mk, Охридско Езеро , al, Liqeni i Ohrit , also referred as ''Liqeni i Pogradecit'';) is a

lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...

which straddles the mountainous border between the southwestern part of

North Macedonia North Macedonia, ; sq, Maqedonia e Veriut, (Macedonia before February 2019), officially the Republic of North Macedonia,, is a country in Southeast Europe. It gained independence in 1991 as one of the successor states of Socialist Feder ...

and eastern

Albania Albania ( ; sq, Shqipëri or ), or , also or . officially the Republic of Albania ( sq, Republika e Shqipërisë), is a country in Southeastern Europe. It is located on the Adriatic and Ionian Seas within the Mediterranean Sea and share ...

. It is one of

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

's deepest and oldest lakes, with a unique aquatic

ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...

of worldwide importance, with more than 200 endemic species. North Macedonia's side of Lake Ohrid was declared a

World Heritage Site A World Heritage Site is a landmark or area with legal protection by an international convention administered by the United Nations Educational, Scientific and Cultural Organization (UNESCO). World Heritage Sites are designated by UNESCO for ...

UNESCO The United Nations Educational, Scientific and Cultural Organization is a List of specialized agencies of the United Nations, specialized agency of the United Nations (UN) aimed at promoting world peace and security through international coope ...

in 1979, with the site being extended to also include the cultural and historic area of Ohrid in 1980. In 2010,

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...

named one of Titan's lakes after it. In 2014, the Ohrid-Prespa Transboundary Reserve between Albania and North Macedonia was added to UNESCO's World Network of Biosphere Reserves. Albania's side of Lake Ohrid was also designated UNESCO world heritage status in 2019. North Macedonia's portion was designated as a protected

Ramsar site A Ramsar site is a wetland site designated to be of international importance under the Ramsar Convention,8 ha (O) *** Permanent 8 ha (P) *** Seasonal Intermittent < 8 ha(Ts) **

Ministry of Environment and Physical Planning (2021)
Ramsar Information Sheet: Lake Ohrid
. Ramsar Secretariat, Gland, Switzerland. In Albania, the coastal portion of the lake holds Managed Nature Reserve status. In North Macedonia, a portion of the lakeside is part of the Galičica National Park. The towns situated at the lakeside are Ohrid and

Struga Struga ( mk, Струга , sq, Strugë) is a town and popular tourist destination situated in the south-western region of North Macedonia, lying on the shore of Lake Ohrid. The town of Struga is the seat of Struga Municipality. Name The n ...

in North Macedonia along with Pogradec in Albania. The lake is otherwise densely surrounded by settlements in the form of villages and resorts in both basin countries.

Geography

Lake Ohrid is one of the oldest lakes in the world, and with a maximum depth of and mean depth of , it is the deepest lake in the

Balkans The Balkans ( ), also known as the Balkan Peninsula, is a geographical area in southeastern Europe with various geographical and historical definitions. The region takes its name from the Balkan Mountains that stretch throughout the who ...

. It covers an area of and contains an estimated 55.4 cubic kilometres ( million

acre-feet The acre-foot is a non- SI unit of volume equal to about commonly used in the United States in reference to large-scale water resources, such as reservoirs, aqueducts, canals, sewer flow capacity, irrigation water, and river flows. An acr ...

) of water. The lake is long and wide at its maximum extent, with a shoreline of . 64% of Lake Ohrid's shoreline and 69% of its surface area are within

, whereas 36% of the shoreline and 31% of its surface area fall within

Origin

The Ohrid and Prespa Lakes are the two largest in a north–south chain of tectonic basins (grabens) including the Korca basin, and Lake Ioannina in NW Greece, known as the Dessaret group. The transition from compressional to extensional tectonics in the central Balkan Mts occurred around 6 million years ago, with the oldest lake sediments being Pliocene, possibly 3-5 million years old. The Dessaret chain is a poorly developed rift valley. Worldwide, rift valley lakes with similarly ancient origins include

Lake Baikal Lake Baikal (, russian: Oзеро Байкал, Ozero Baykal ); mn, Байгал нуур, Baigal nuur) is a rift lake in Russia. It is situated in southern Siberia, between the federal subjects of Irkutsk Oblast to the northwest and the ...

, Lake Titicaca,

Lake Tanganyika Lake Tanganyika () is an African Great Lake. It is the second-oldest freshwater lake in the world, the second-largest by volume, and the second-deepest, in all cases after Lake Baikal in Siberia. It is the world's longest freshwater lake. T ...

and the Dead Sea. Most lakes have much shorter life spans as they rapidly fill with sediments. Lake Ohrid is being infilled at its north end by its modest main tributaries, but is preserved by its great depth, by continuing tectonic subsidence, and by the main inflows being by underground karstic channels from Lake Prespa carrying minimal sediment. The

graben In geology, a graben () is a depressed block of the crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German, meaning 'ditch' or 'trench'. The word was first used in the geologic conte ...

system is still tectonically active and Lake Ohrid sits in a seismogenic landscape, with many visible traces including fresh fault scarps, displaced sediment and soil sequences, stepped hillsides, and a hydrothermal field near Kosel. Moderate earthquakes are frequent, with the strongest yet measured here on 18 February 1911, with a magnitude 6.6 at a focal depth of 15 km, destroying houses but with no loss of life

Hydrology

The lake drains an area of around 2,600 km² and is fed primarily by underground springs on the eastern shore (about 50% of total inflow), with roughly 25% shares from rivers and direct precipitation. Over 20% of the lake's water comes from nearby Lake Prespa, about to the southeast and at 150 m higher altitude than Lake Ohrid. The water leaves Lake Prespa trickling through underground watercourses in the

karst Karst is a topography formed from the dissolution of soluble rocks such as limestone, Dolomite (rock), dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. It has also been documented for more weathe ...

ic landscape, where it is joined by mountain range precipitation and eventually emerges in numerous springs along the eastern shore and below the water surface of Lake Ohrid. The water leaves Lake Ohrid by

evaporation Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. High concentration of the evaporating substance in the surrounding gas significantly slows down evaporation, such as when h ...

(~40%) and through its only outlet, the Black Drin River, which flows in a northerly direction into

and thus to the

Adriatic Sea The Adriatic Sea () is a body of water separating the Italian Peninsula from the Balkan Peninsula. The Adriatic is the northernmost arm of the Mediterranean Sea, extending from the Strait of Otranto (where it connects to the Ionian Sea) to th ...

. The relatively dry, Mediterranean climate and the small drainage basin of 2,600 km² (catchment/lake surface ratio of ~7) of Lake Ohrid results in a long hydraulic residence time scale of ~70 yr.Z. Spirkovski, Z. Krstanovski, L. Selfo, M. Sanxhaku, V.I. Puka, "The Monitoring Programme of the Lake Ohrid Conservation Project", in ''Transboundary Water Resources in the Balkans: Initiating a Sustainable Co-Operative Network'', ed. Jacques Ganoulis, I L Murphy, Mitja Brilly (Springer, 2000)A. Matzinger, Z. Spirkovski, S. Patceva, A. Wüest, "Sensitivity of ancient Lake Ohrid to local anthropogenic impacts and global warming" (Journal of Great Lakes Research 2006, 32: 158–179)A. Matzinger, M. Jordanoski, E. Veljanoska-Sarafiloska, M. Sturm, B. Müller, A. Wüest, "Is Lake Prespa jeopardizing the ecosystem of ancient Lake Ohrid?" (Hydrobiologia 2006, 553: 89–109)

Physical and geochemical properties

The water at the surface of Lake Ohrid moves predominantly in a counter-clockwise direction along the shore, as a result of wind forcing and the Earth rotation, similar to the Ekman-phenomenon known from oceans. In terms of vertical water exchange,

convective Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the ...

mixing during winter cooling is the dominant process. However, in an average winter only the top 150–200 meters of the lake are mixed, whereas the water below is stably

stratified Stratification may refer to: Mathematics * Stratification (mathematics), any consistent assignment of numbers to predicate symbols * Data stratification in statistics Earth sciences * Stable and unstable stratification * Stratification, or st ...

by salinity. The stability due to this salinity gradient allows complete convective mixing events only roughly once every 7 years.S. D. Hadzisce, "The mixo-phenomenon of Lake Ohrid in the course of the years 1941/42-1964/65 (in German)" (Proceedings of the International Association of Theoretical and Applied Limnology 1966, 16: 134–138) Both in terms of

nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excre ...

concentration (4.5 μg L⁻¹ of phosphorus), as well as biological parameters Lake Ohrid qualifies as oligotrophic. Thanks to this oligotrophy and the filtered spring inflows, the water is exceptionally clear with transparencies to a depth of as much as 22 meters (66 feet). Lake Ohrid lacks an annual deep water exchange which in other lakes can bring complete overturn; plunging rivers are also absent. Despite this, dissolved oxygen never drops below ~6 mg L⁻¹.A. Matzinger, M. Schmid, E. Veljanoska-Sarafiloska, S. Patceva, D. Guseska, B. Wagner, B. Müller, M. Sturm, A. Wüest, M. Watzin, V. Puka, T. B. Naumoski (eds), "Lake Ohrid and its watershed, state of the environment report" (Lake Ohrid Conservation Project. Tirana, Albania and Ohrid, Macedonia)

Wetland habitats

Previously extensive wetland habitats in the vicinity of Lake Ohrid have been lost due to conversion into agricultural or urban land. These include Struga Marsh, large portions of which were drained for agriculture in the 1940s and again in the 1960s when the River Sateska was rerouted.Deutsche Gesellschaft für Internationale Zusammenarbeit (2015)
nitial Characterisation of Lakes Prespa, Ohrid and Shodra/Skadar. Implementing the EU Water Framework Directive in South-Eastern Europe
. Nowadays, the last remaining significant coastline wetland at Lake Ohrid is Studenchishte Marsh, which is located on the eastern shore near the city of Ohrid. Despite degradation from a variety of sources such as large-scale disposal of construction waste, major land conversion, disruption of water connections to Lake Ohrid, beach urbanization and loss of reed belts, Studenchishte Marsh is still an important buffer to prevent lake eutrophication and a key habitat for biodiversity, including relict plants and endemic species. These values, and the comparative rareness of similar habitats in Macedonia (now North Macedonia), prompted an expert team in 2012 to recommend designation of a 63.97-hectare area at Studenchishte Marsh to be protected as a Natural Monument under Macedonian law. Changes to the General Urban Plan for Ohrid 2014–2020, however, made provisions for Studenchishte Marsh to be drained and replaced with infrastructure for tourism and water-sports, a proposal which, together with other regional developments, was opposed by numerous local and international experts, including the Society of Wetland Scientists. A Strategic Environmental Assessment also concluded that no measure except non-implementation could reduce the direct negative impact on Studenchishte and the indirect negative impact on Lake Ohrid if the proposed construction was to take place at the wetland. Plans to drain the area have subsequently been reversed and the Macedonian government announced in 2018 that it would move forward with proclamation of Studenchishte Marsh as a protected area and its designation together with Lake Ohrid as a Wetland of International Importance under the Ramsar Convention. Ramsar status was formalized in 2021 although protection of Studenchishte Marsh at the national level has not yet been completed. The

IUCN The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...

identifies wetland rehabilitation as one of five potential site needs for the

Natural and Cultural Heritage of the Ohrid Region.International Union for the Conservation of Nature (IUCN) (2017
Natural and Cultural Heritage of the Ohrid region 2017 Conservation Outlook Assessment
Gland, Switzerland. However, the potential to restore Struga Marsh, which was not included in the boundaries of the Ramsar Site, is likely to be reduced by construction of the European Corridor VIII railway, while Studenchishte's future is yet to be fully resolved.World Heritage Centre, ICOMOS and IUCN (2017
Reactive Monitoring Mission Report Natural and Cultural Heritage of the Ohrid Region (Former Yugoslav Republic of Macedonia)
World Heritage Centre, Paris, France.

Fauna

Measured by its surface area of 358 km², Ohrid is probably the most biodiverse lake on Earth.Albrecht, Christian and Wilke, Thomas: ''Ancient Lake Ohrid: biodiversity and evolution; in Patterns and Processes of Speciation in Ancient Lakes'', Developments in Hydrobiology, Springer Netherlands, 2009, pp 103 to 140. While it is special as such, by far the most spectacular quality is its impressive

endemism Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found els ...

. Similar to

, Lake Ohrid harbors endemic species covering the whole food-chain, from

phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words (), meaning 'plant', and (), meaning 'wanderer' or 'drifter'. ...

and sessile algae (20 species; e.g., ''

Cyclotella fottii ''Cyclotella'' is a genus of diatoms often found in oligotrophic environments, both marine and fresh water. It is in the family Stephanodiscaceae and the order Thalassiosirales. The genus was first discovered in the mid 1800s and since then has ...

''), over plant species (2 species; e.g., '' Chara ohridana''),

zooplankton Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...

(5 species; e.g., ''

Cyclops ochridanus In Greek mythology and later Roman mythology, the Cyclopes ( ; el, Κύκλωπες, ''Kýklōpes'', "Circle-eyes" or "Round-eyes"; singular Cyclops ; , ''Kýklōps'') are giant one-eyed creatures. Three groups of Cyclopes can be distinguish ...

''),

cyprinid Cyprinidae is a family of freshwater fish commonly called the carp or minnow family. It includes the carps, the true minnows, and relatives like the barbs and barbels. Cyprinidae is the largest and most diverse fish family and the largest ...

fish (8 species; e.g., '' Pachychilon pictus''), to predatory fish (two trout species; the Ohrid trout complex ''Salmo letnica'', and "Belvica" '' Salmo ohridanus'') and finally its diverse endemic bottom fauna (176 species; e.g. '' Ochridagammarus solidus''), with particularly large endemism among

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapoda, decapods, ostracoda, seed shrimp, branchiopoda, branchiopods, argulidae, fish lice, krill, remipedes, isopoda, isopods, barnacles, copepods, ...

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is est ...

s, sponges and planarians. There were recorded 68 species of

freshwater snail Freshwater snails are gastropod mollusks which live in fresh water. There are many different families. They are found throughout the world in various habitats, ranging from ephemeral pools to the largest lakes, and from small seeps and springs ...

s from the Lake Ohrid basin. 73.5% (50 species) of the total freshwater gastropod fauna appear to be endemic to the Lake Ohrid basin. Whereas the endemic species list cited above is based on morphological and ecological characteristics, some recent applications of molecular genetic techniques underline the difference of the fauna from common European taxa, as well as the old age of the lake.S. Stankovic, "The Balkan Lake Ohrid and its living world", Monographiae Biologicae, Vol. IX (Uitgeverij Dr. W. Junk, Den Haag, Netherlands, 1960)H. Salemaa, "Lake Ohrid", in ''Speciation in Ancient Lakes'', eds. K. Martens, B. Goddeeris, G. Coulter (Archiv für Hydrobiologie – Advances in Limnology 1994, 44: 55–64) Quite remarkably, exotic species do not seem to be a major issue in Lake Ohrid, although they have been recorded in small populations for several decades or exist in nearby rivers or lakes. The reason lies very probably in the ideal adaptation of the endemic species to the specific conditions in the lake, such as low nutrient availability, good living conditions in greater depth thanks to high water transparency and oxygen content, as well as subaquatic spring inflows supplying cool and

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...

-rich water. In total, seven introduced fish species are known from the lake. Despite the exceptionally high level of endemism in Lake Ohrid (for example, a third of the 21 native fish species and almost 80% of its 72 mollusc species are endemic), a significant number of non-endemic species are found in Lake Ohrid. This includes species, which are mobile (e.g., via water birds) or migratory, such as the

European eel The European eel (''Anguilla anguilla'') is a species of eel, a snake-like, catadromous fish. They are normally around and rarely reach more than , but can reach a length of up to in exceptional cases. Eels have been important sources of ...

Birds

The lakeshore reed beds and wetlands provide critical habitat for hundreds of thousands of wintering water birds, including rare and threatened species such as the Dalmatian pelican, ferruginous duck,

swan Swans are birds of the family Anatidae within the genus ''Cygnus''. The swans' closest relatives include the geese and ducks. Swans are grouped with the closely related geese in the subfamily Anserinae where they form the tribe Cygnini. Som ...

, spotted eagle, and eastern imperial eagle. The Macedonian part of the lake has been designated an

Important Bird Area An Important Bird and Biodiversity Area (IBA) is an area identified using an internationally agreed set of criteria as being globally important for the conservation of bird populations. IBA was developed and sites are identified by BirdLife Inte ...

(IBA) by

BirdLife International BirdLife International is a global partnership of non-governmental organizations that strives to conserve birds and their habitats. BirdLife International's priorities include preventing extinction of bird species, identifying and safeguarding ...

because it supports populations of

common coot The Eurasian coot (''Fulica atra''), also known as the common coot, or Australian coot, is a member of the rail and crake bird family, the Rallidae. It is found in Europe, Asia, Australia, New Zealand and parts of North Africa. It has a slaty-bla ...

s and pygmy cormorants (''Microcarbo pygmaeus''). The Albanian part of the lake has been designated a separate but corresponding IBA for the same reason, with additional bird species being common goldeneyes, red-crested pochards (''Netta rufina'') and black-necked grebes. Wetland of International Importance status under the Ramsar Convention is underpinned in part by the biogeographically significant populations of red-crested pochard and pygmy cormorants too, but also

goosander The common merganser (North American) or goosander (Eurasian) (''Mergus merganser'') is a large seaduck of rivers and lakes in forested areas of Europe, Asia, and North America. The common merganser eats mainly fish. It nests in holes in trees. ...

(''Mergus merganser'').

Socio-economy

There are three cities on the lake's shores: Ohrid and

on the Macedonian side; and Pogradec in Albania. There are also several fishing villages, although tourism is now a more significant part of their income. The catchment area of the lake has a population of around 170,000 people, with 131,000 people living directly at the lake shore (43,000 in Albania and 88,000 in North Macedonia). The population in the catchment has increased by 100,000 people in the last half century, putting the lake's fragile ecosystem under pressure. The historic monuments, as well as the pristine lake environment, make the area around Lake Ohrid a prime site for tourism. In the 1980s, more than 200,000 national and international tourists went on a pilgrimage to the Macedonian lake side every year. During the Yugoslav crisis and particularly after the interethnic conflicts within North Macedonia in 2001, international tourism collapsed but has been slowly recovering. Even though many visitors are staying for a weekend only, tourism makes an important contribution to the local economy (~1 visitor/inhabitant). Historically, Lake Ohrid was close to a main highway of the Roman Empire, the Via Egnatia, from Durrës on the coast of Albania to Thessalonika and Constantinople (Istanbul), but now is a communications backwater. There is a minor road around the lake, with border crossings between Albania and North Macedonia. Religious monuments such as the Black Madonna south west of Struga and St Naum monastery are counterposed with ravages of war, such as the fortifications of the Macedonian Front across Galicica Mountain.

World Heritage Site

Fortaleza de Samuel, Ohrid, Macedonia, 2014-04-17, DD 47

The Macedonian side of Lake Ohrid was declared a World Heritage Site by UNESCO at the 3rd Session of the

World Heritage Committee The World Heritage Committee selects the sites to be listed as UNESCO World Heritage Sites, including the World Heritage List and the List of World Heritage in Danger, defines the use of the World Heritage Fund and allocates financial assistance ...

in 1979 and holds that status under Criterion VII as a superlative natural phenomenon related to its refuge function for relict and world-unique freshwater species, and its rich bird life. The lake became part of a mixed Natural and Cultural World Heritage Site in 1980 when the city of Ohrid in Macedonia was also designated with UNESCO status for its architectural, artistic and religious values. Concern over current and potential deterioration of the World Heritage Site prompted invitation of a joint Reactive Monitoring Mission by the World Heritage Centre, IUCN and ICOMOS in April 2017, which identified a wide range of pressures including from transport infrastructure, traffic, tourism developments, overfishing, sewerage, solid waste disposal, invasive species, both legal and illegal construction, and management of water levels. The mission report devised 19 recommendations for Macedonia, which were incorporated under Decision 41 COM 7B.34 of the World Heritage Committee at its 41st Session in Krakow, Poland in 2017. In May 2019, the UNESCO World Heritage Centre expanded the World Heritage Site to the Albanian side of the lake. In addition, draft Decision 43 COM 7B.36 was released recommending for the Ohrid region, including Lake Ohrid, to be placed on the List of World Heritage in Danger during the 43rd Session of the

in Baku, Azerbaijan. This position aligns with IUCN advice. In its analysis and conclusions, the World Heritage Centre observed threats to Lake Ohrid from "decreased water levels, uncontrolled discharge, water pollution due to inadequate wastewater treatment systems leading to evident eutrophication at the mouths of intake rivers, heavy pressures from tourism, and extensive uncontrolled urban development and inappropriate exploitation of the coastal zones." It also observed that the majority of recommendations from the 2017 Reactive Monitoring Mission had not been implemented.

Science and research

Due to its size, accessibility and species richness, Lake Ohrid is extremely well-suited to the function of a natural laboratory. Deep sediment cores augmented by diverse ecology in the present day offer an extensive archive from which to understand the history of its region over the past 1,200,000 years. Research to date has investigated biodiversity processes, the interplay between geological and biological evolution, the birth of European agriculture, and investigations of regional climate and environmental conditions over hundreds of thousands of years. Among other contributions, such research has delivered the first empirical evidence for niche-based assembly processes from a natural system and demonstrated the establishment of dynamic equilibrium in an isolated ecosystem during the slowdown of both speciation and extinction rates. It has also demonstrated the importance of tree cover for buffering soil erosion during times of climate change and provided insight into the composition of regional flora through glacial and inter-glacial periods.

Human influence

Shore habitats are under particular pressure from human activities. Particular threats are the building of tourist facilities directly at the shore, destroying of reed belts to gain agricultural land and intense pollution close to the mouth of tributaries. Although the effects of these human impacts have not been evaluated in detail they are of great concern, as the shallow water sites are particularly rich in endemic bottom fauna and form important spawning grounds for several endemic fish species. Moreover, reed belts have great importance for water birds. Commercial fish yield, i.e. the two endemic

trout Trout are species of freshwater fish belonging to the genera '' Oncorhynchus'', '' Salmo'' and '' Salvelinus'', all of the subfamily Salmoninae of the family Salmonidae. The word ''trout'' is also used as part of the name of some non-salm ...

species, has dropped significantly over the past decades, both in North Macedonia and in Albania. The most probable reason is

overfishing Overfishing is the removal of a species of fish (i.e. fishing) from a body of water at a rate greater than that the species can replenish its population naturally (i.e. the overexploitation of the fishery's existing fish stock), resulting in t ...

and possibly destruction of spawning grounds. Pollution may also be a factor. Although there are regulations regarding fishing practice (e.g. minimal mesh size) and only a limited number of licensed fishermen, these rules are always not obeyed as a result of the high market value of the endemic trout. As a reaction to the situation, a seven-year moratorium on fishing Ohrid trout was imposed from 2004 to help the population recover and to allow scientists collect further data. Nonetheless, even though thorough assessment of fish stocks has not been conducted since the 1990s and trout populations are still believed to be in decline, fishing with quotas was restarted in 2012 under the auspices of a concessionaire. More data is required to determine whether these current fishing levels are sustainable and illegal fishing, particularly on the Albanian side of the lake, remains a problem. While most of the endemic fish species are non-migratory, the

spawns in the distant

Sargasso Sea The Sargasso Sea () is a region of the Atlantic Ocean bounded by four currents forming an ocean gyre. Unlike all other regions called seas, it has no land boundaries. It is distinguished from other parts of the Atlantic Ocean by its charac ...

while its offspring return to the lake. Unfortunately, as in many European lakes, it is very unlikely today that eels can reach Lake Ohrid naturally and return to the

, as a result of several hydropower dams on the Black Drin and the Drin River, both in North Macedonia and Albania. As a result, eel found in Lake Ohrid are stocked populations. Pogradec, Lake Ohrid - Albania

Given the population growth over the past 50 years, a particular concern is the potential

eutrophication Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phyt ...

of currently oligotrophic Lake Ohrid from increased pollution. Indeed,

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand ...

cores show a ~3.5 fold increase in

phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ea ...

concentration over the past century. On the one hand, shifts from endemic to common European species, which are better adapted to higher nutrient conditions, have already been observed close to polluted inflows. On the other hand, higher nutrient levels have reduced the water transparency, as well as the oxygen availability in the deep water and at the lake bottom, two properties which are requisite for the endemic flora and fauna. Still, the lake is in a comparably good state at the moment. However it may take more than a decade to see the effects of today's pollution level in the lake, because of its long water residence time. Moreover, it was shown that the negative effects from eutrophication would be significantly amplified by

global warming In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...

. Although there is time to react, computer simulations indicate that at least a 50% reduction in phosphorus input must be reached to keep the deep water oxygenated for the next 50 years at predicted atmospheric warming. This aim could be reached by controlling household wastewater, which is by far the biggest phosphorus source at the moment. First steps in that direction have been taken by extending and improving the existing sewage system in North Macedonia in the framework of a GEF (

Global Environment Facility The Global Environment Facility (GEF) is a multilateral environmental fund that provides grants and blended finance for projects related to biodiversity, climate change, international waters, land degradation, persistent organic pollutants (PO ...

) program. The most important next task would be a solution for three remaining, severely polluted tributaries, one in North Macedonia and two in Albania.

Declaration on the Protection of the Lake Ohrid Ecosystem

On 3 May 2018, the Society of Wetland Scientists released the Declaration on the Protection of the Lake Ohrid Ecosystem, which was passed unanimously by 45 attending members at its 13th annual Europe meeting. Urging Macedonian authorities to substantially enhance protection of Lake Ohrid, the declaration outlines the unique significance of the interconnected Ohrid-Prespa lake system, both for its biodiversity and relevance to research on climate and evolution, and recommends measures for future management including revitalization and enlargement of wetland areas, pollution control and a re-orientation of tourism policy.Society of Wetland Scientists (2018) The Declaration on The Protection of the Lake Ohrid Ecosystem (Available 28/5/2018 via http://www.sws.org/images/chapters/europe/Declaration.pdf) It further describes the "critical importance" of the last intact marsh on the Lake Ohrid shore, Studenchishte Marsh, in terms of its species composition and ecosystem services such as water quality improvement, carbon storage and flood retention among others.

Namesakes

Lake Ohrid is also the namesake of

Ohrid Lacus Ohrid ( mk, Охрид ) is a city in North Macedonia and is the seat of the Ohrid Municipality. It is the largest city on Lake Ohrid and the eighth-largest city in the country, with the municipality recording a population of over 42,000 inhab ...

, a

hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...

lake on the

Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...

ian moon

Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictiona ...

. It is composed of

liquid A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, ...

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane ...

and

ethane Ethane ( , ) is an organic chemical compound with chemical formula . At standard temperature and pressure, ethane is a colorless, odorless gas. Like many hydrocarbons, ethane is isolated on an industrial scale from natural gas and as a petroc ...

and is located 71.8° N 221.9° W on

's globe.