The Ombla is a short river in

Croatia , image_flag = Flag of Croatia.svg , image_coat = Coat of arms of Croatia.svg , anthem = "Lijepa naša domovino"("Our Beautiful Homeland") , image_map = , map_caption = , capit ...

, northeast of

Dubrovnik Dubrovnik (), historically known as Ragusa (; see notes on naming), is a city on the Adriatic Sea in the region of Dalmatia, in the southeastern semi-exclave of Croatia. It is one of the most prominent tourist destinations in the Mediterran ...

. Its course is approximately long, and it empties into the

Rijeka Dubrovačka Rijeka Dubrovačka (Italian: ''Val d'Ombla'') is a ria (coastal inlet) to the north of Dubrovnik, Croatia, on the coast of the Adriatic Sea. The Ombla The Ombla is a short river in Croatia, northeast of Dubrovnik. Its course is approximately lo ...

ria A ria (; gl, ría) is a coastal inlet formed by the partial submergence of an unglaciated river valley. It is a drowned river valley that remains open to the sea. Definitions Typically rias have a dendritic, treelike outline although they ca ...

formed by 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 t ...

near

Komolac Komolac is one of two city districts Dubrovnik, Croatia , image_flag = Flag of Croatia.svg , image_coat = Coat of arms of Croatia.svg , anthem = "Lijepa naša domovino"("Our Beautiful Homeland") , image_m ...

Dubrovnik-Neretva County The Dubrovnik-Neretva County (; hr, Dubrovačko-neretvanska županija, ) is the southernmost county of Croatia, located in south Dalmatia. The county seat is Dubrovnik and other large towns are Korčula, Metković, Opuzen and Ploče. The Munici ...

. Rijeka Dubrovačka is actually a

, a flooded river valley formed through changes in sea surface elevation on a

geologic time scale The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochrono ...

. The river rises as a

karst spring A karst spring or karstic spring is a spring (outflow of groundwater) that is part of a karst hydrological system. Description Because of their often conical or inverted bowl shape, karst springs are also known in German-speaking lands as a ''Top ...

fed by

groundwater Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...

replenished by

Trebišnjica The Trebišnjica ( sr-cyrl, Требишњица) is a river in Bosnia and Herzegovina. It used to be a sinking river, long above the ground. With a total length of above and under the ground, it is one of the longest sinking rivers in the world ...

, which is an influent stream flowing in

Popovo Polje Popovo field ( sh-Latn-Cyrl, separator=" / ", Popovo polje, Попово поље, , ) is a ''polje'' ( karstic field) in Bosnia and Herzegovina, located in a southernmost region of the country, near the Adriatic coast. Its size is . Popovo polj ...

, in the immediate hinterland of the Ombla. The elevation difference between the river's source and its mouth is just over . The average discharge of the river is per second. The drainage basin of the Ombla encompasses and, besides the short surface course, includes only groundwater flow. The Ombla is used as a source of

drinking water Drinking water is water that is used in drink or food preparation; potable water is water that is safe to be used as drinking water. The amount of drinking water required to maintain good health varies, and depends on physical activity level, a ...

for Dubrovnik's

water supply network A water supply network or water supply system is a system of engineered hydrologic and hydraulic components that provide water supply. A water supply system typically includes the following: # A drainage basin (see water purification – source ...

, and construction of a

hydroelectric power plant Hydroelectricity, or hydroelectric power, is electricity generated from hydropower (water power). Hydropower supplies one sixth of the world's electricity, almost 4500 TWh in 2020, which is more than all other renewable sources combined an ...

has been planned for the past two decades. , the plans entail construction of a subsurface

reservoir A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation. Reservoirs can be created in a number of ways, including contro ...

and a 68

megawatt The watt (symbol: W) is the unit of Power (physics), power or radiant flux in the International System of Units, International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantification (science), ...

power plant. The plan sparked controversy amid doubts raised with respect to

environmental protection Environmental protection is the practice of protecting the natural environment by individuals, organizations and governments. Its objectives are to conserve natural resources and the existing natural environment and, where possible, to repair dam ...

and

biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') l ...

management, technical and financial feasibility, and procedural problems related to the project. A particular concern expressed was that the underground reservoir might trigger earthquakes.

Source and course

The course of the Ombla River is located in the

, northeast of the city of

in the southernmost part of the mainland of

Croatia , image_flag = Flag of Croatia.svg , image_coat = Coat of arms of Croatia.svg , anthem = "Lijepa naša domovino"("Our Beautiful Homeland") , image_map = , map_caption = , capit ...

. The entire

with its surroundings bears the name,

(lit. ''Dubrovnik's River''), and encompasses several villages clustered near the Ombla that are home to 12,000 people. The name is also applied to an

estuary An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environment ...

of the Ombla—a

enclosed by steep slopes of high hills, forming a long, wide and deep

embayment A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean, a lake, or another bay. A large bay is usually called a gulf, sea, sound, or bight. A cove is a small, circular bay with a narr ...

of the

. The Ombla rises at the foot of the Golubov Kamen

massif In geology, a massif ( or ) is a section of a planet's crust that is demarcated by faults or flexures. In the movement of the crust, a massif tends to retain its internal structure while being displaced as a whole. The term also refers to a ...

, a landform that straddles the border between Croatia and

Bosnia-Herzegovina Bosnia and Herzegovina ( sh, / , ), abbreviated BiH () or B&H, sometimes called Bosnia–Herzegovina and Pars pro toto#Geography, often known informally as Bosnia, is a country at the crossroads of Southern Europe, south and southeast Euro ...

. The river rises in an cave whose roof has an clearance above the surface of the water. The primary source is located at an elevation of

below sea level This is a list of places on land below mean sea level. Places artificially created such as tunnels, mines, basements, and dug holes, or places under water, or existing temporarily as a result of ebbing of sea tide etc., are not included. Places ...

, and the secondary sources are found at

above sea level Height above mean sea level is a measure of the vertical distance (height, elevation or altitude) of a location in reference to a historic mean sea level taken as a vertical datum. In geodesy, it is formalized as ''orthometric heights''. The comb ...

(a.s.l.). The spring is the largest

in Croatia, and one of the largest ones in the

Dinarides The Dinaric Alps (), also Dinarides, are a mountain range in Southern and Southcentral Europe, separating the continental Balkan Peninsula from the Adriatic Sea. They stretch from Italy in the northwest through Slovenia, Croatia, Bosnia and Herz ...

. The surface of the water in the cave is a.s.l. The watercourse flows for approximately before reaching a

weir A weir or low head dam is a barrier across the width of a river that alters the flow characteristics of water and usually results in a change in the height of the river level. Weirs are also used to control the flow of water for outlets of l ...

across which the Ombla discharges into the Adriatic Sea, leading to claims that the Ombla is the shortest river in the world.

Drainage basin

The

drainage basin A drainage basin is an area of land where all flowing surface water converges to a single point, such as a river mouth, or flows into another body of water, such as a lake or ocean. A basin is separated from adjacent basins by a perimeter, t ...

of the Ombla is estimated to cover an area of at least , and up to between the Adriatic Sea coast in the area of Dubrovnik and

. Other than the short surface course of the river, the drainage basin includes

only. The exact boundaries of the drainage basin vary depending on prevailing hydrological conditions determining groundwater

seepage Soil mechanics is a branch of soil physics and applied mechanics that describes the behavior of soils. It differs from fluid mechanics and solid mechanics in the sense that soils consist of a heterogeneous mixture of fluids (usually air and wat ...

and flow. The area comprises 176 settlements and 50,000 inhabitants. The area exhibits

karst Karst is a topography formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum. It is characterized by underground drainage systems with sinkholes and caves. It has also been documented for more weathering-resistant ro ...

morphology, with

bedrock In geology, bedrock is solid Rock (geology), rock that lies under loose material (regolith) within the crust (geology), crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface mater ...

largely consisting of

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

s and comparatively small areas of

dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

s and

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...

sediments.

Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...

flysch Flysch () is a sequence of sedimentary rock layers that progress from deep-water and turbidity flow deposits to shallow-water shales and sandstones. It is deposited when a deep basin forms rapidly on the continental side of a mountain building epi ...

forms the southwest boundary of the catchment area, towards which the catchment basin drains and where the Ombla rises. The rocks were formed as a thick series of carbonate sediments were deposited between the

Norian The Norian is a division of the Triassic Period. It has the rank of an age (geochronology) or stage (chronostratigraphy). It lasted from ~227 to million years ago. It was preceded by the Carnian and succeeded by the Rhaetian. Stratigraphic defi ...

and

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...

as the

Adriatic Carbonate Platform The Adriatic Sea () is a body of water separating the Italian Peninsula from the Balkans, 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) ...

, up to deep. In the Eocene and early

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

, the

Adriatic Plate The Adriatic or Apulian Plate is a small tectonic plate carrying primarily continental crust that broke away from the African Plate along a large transform fault in the Cretaceous period. The name Adriatic Plate is usually used when referring ...

moved north and north-east, contributing to the Alpine orogeny via the

tectonic uplift Tectonic uplift is the geologic uplift of Earth's surface that is attributed to plate tectonics. While isostatic response is important, an increase in the mean elevation of a region can only occur in response to tectonic processes of crustal thick ...

of the

. The basin's karst topography developed from the carbonate platform's exposure to

weathering Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little or no movement), ...

. Karstification largely began after the Dinarides' final uplift in the Oligocene and the

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

, when the carbonates were exposed to atmospheric effects; this extended to the level of below the present sea level, exposed during the

Last Glacial Maximum The Last Glacial Maximum (LGM), also referred to as the Late Glacial Maximum, was the most recent time during the Last Glacial Period that ice sheets were at their greatest extent. Ice sheets covered much of Northern North America, Northern Eur ...

. Some karst formations were created during earlier sea level drops, most notably the

Messinian salinity crisis The Messinian salinity crisis (MSC), also referred to as the Messinian event, and in its latest stage as the Lago Mare event, was a geological event during which the Mediterranean Sea went into a cycle of partial or nearly complete desiccation (dr ...

. The geological structure of the area indicates recent tectonic activity in the catchment, with a fault running between

Hum Hum may refer to: Science * Hum (sound), a sound produced with closed lips, or by insects, or other periodic motion * Mains hum, an electric or electromagnetic phenomenon * The Hum, an acoustic phenomenon * Venous hum, a physiological sensation ...

and the Ombla. A recent strong earthquake in the wider region was the 1979 Montenegro earthquake, measuring 7.0 on the

Richter scale The Richter scale —also called the Richter magnitude scale, Richter's magnitude scale, and the Gutenberg–Richter scale—is a measure of the strength of earthquakes, developed by Charles Francis Richter and presented in his landmark 1935 ...

. The only strong historical earthquake in the immediate area was the 1667 Dubrovnik earthquake, which was followed by a

tsunami A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explo ...

. The hydrological regime of the basin and Popovo Polje is determined by the flow of the

—a

losing stream A losing stream, disappearing stream, influent stream or sinking river is a stream or river that loses water as it flows downstream. The water infiltrates into the ground recharging the local groundwater, because the water table is below the bo ...

disappearing underground in the

polje A polje, also karst polje or karst field, is a large flat plain found in karstic geological regions of the world, with areas usually . The name derives from the Slavic languages and literally means 'field', whereas in English ''polje'' specific ...

. The groundwater is distributed to a number of springs. Some of them are

headwaters The headwaters of a river or stream is the farthest place in that river or stream from its estuary or downstream confluence with another river, as measured along the course of the river. It is also known as a river's source. Definition The ...

of watercourses discharging into the Neretva River to the northwest of the polje, or appearing as vruljas (submarine springs) or as headwaters of the Ombla river. Flow rate of the Ombla River, measured at the

water intake A water supply network or water supply system is a system of engineered hydrologic and hydraulic components that provide water supply. A water supply system typically includes the following: # A drainage basin (see water purification – source ...

plant, ranges from per second, averaging per second. The average has dropped by about per second since completion of Trebišnjica Hydroelectric Power Plant and the concreting of the Trebišnjica's

river bed A stream bed or streambed is the bottom of a stream or river (bathymetry) or the physical confine of the normal water flow ( channel). The lateral confines or channel margins are known as the stream banks or river banks, during all but flood ...

. On the other hand, the minimum discharge was not affected by the

river engineering River engineering is a discipline of civil engineering which studies human intervention in the course, characteristics, or flow of a river with the intention of producing some defined benefit. People have intervened in the natural course and b ...

works. The catchment basin area straddles boundary of two

climate zone Climate classifications are systems that categorize the world's climates. A climate classification may correlate closely with a biome classification, as climate is a major influence on life in a region. One of the most used is the Köppen climate ...

s—the

Mediterranean climate A Mediterranean climate (also called a dry summer temperate climate ''Cs'') is a temperate climate sub-type, generally characterized by warm, dry summers and mild, fairly wet winters; these weather conditions are typically experienced in the ...

zone in areas at

elevation The elevation of a geographic location is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface (see Geodetic datum § Vert ...

s up to a.s.l, and the

continental climate Continental climates often have a significant annual variation in temperature (warm summers and cold winters). They tend to occur in the middle latitudes (40 to 55 north), within large landmasses where prevailing winds blow overland bringing som ...

zone in other parts of the basin. Average annual

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...

varies depending on the climate zones: in Dubrovnik, at the coast, and in Hum, in Popovo Polje.

Economy

, the Ombla is used as a source of

for the city of Dubrovnik. The water intake plant at Komolac has a water supply capacity of per second. The Ombla has been used as a part of Dubrovnik's

since 1897, when the first contract to supply of water per day was made with an owner of

watermill A watermill or water mill is a mill that uses hydropower. It is a structure that uses a water wheel or water turbine to drive a mechanical process such as milling (grinding), rolling, or hammering. Such processes are needed in the production of ...

s operating on the river. The river water becomes opaque, containing increased proportion of suspended particulate matter, three to five times a year for periods of four to five days after increased rainfall. The situation is proposed to be addressed through moving of the intake plant to a higher elevation during construction of a proposed Ombla

Hydroelectric Power Plant Hydroelectricity, or hydroelectric power, is electricity generated from hydropower (water power). Hydropower supplies one sixth of the world's electricity, almost 4500 TWh in 2020, which is more than all other renewable sources combined an ...

(HPP). The new water intake is planned to be constructed at a.s.l. These changes are expected to improve the quality of the drinking water, and to increase the water supply capacity to per second. Average volume of water diverted to the water supply network varies considerably by month, peaking during summer tourist seasons. In August 2008, daily volume of water taken from Ombla for the water supply network averaged at . In 2008, the annual daily volume of the water diverted averaged .

Proposed power plant

The Ombla HPP is proposed to be built as an underground power plant utilizing headwaters of the Ombla River through a planned underground reservoir, which would hold the water behind a

grout curtain A grout curtain is a barrier that protects the foundation of a dam from seepage and can be made during initial construction or during repair. Additionally, they can be used to strengthen foundations and contain spills. Characteristics A grout curt ...

and a concrete block extending from below sea level to a.s.l. The project entails flooding of a cavern system at the spring to a level below the entrance to the long Vilina Cave. The proposed power plant is planned to have

productive capacity Productive capacity is the maximum possible output of an economy. According to the United Nations Conference on Trade and Development (UNCTAD), no agreed-upon definition of maximum output exists. UNCTAD itself proposes: "the productive ''resources'' ...

of 68

s. The project is to be financed in part through a

European Bank for Reconstruction and Development The European Bank for Reconstruction and Development (EBRD) is an international financial institution founded in 1991. As a multilateral developmental investment bank, the EBRD uses investment as a tool to build market economies. Initially focus ...

(EBRD) loan in the amount of 123.2 million

Euro The euro ( symbol: €; code: EUR) is the official currency of 19 out of the member states of the European Union (EU). This group of states is known as the eurozone or, officially, the euro area, and includes about 340 million citizens . ...

s, approved on 22 November 2011. Total project cost is estimated at 152.4 million Euros. Pursuant to the

European Union The European Union (EU) is a supranational political and economic union of member states that are located primarily in Europe. The union has a total area of and an estimated total population of about 447million. The EU has often been des ...

Habitats Directive The Habitats Directive (more formally known as Council Directive 92/43/EEC on the Conservation of natural habitats and of wild fauna and flora) is a directive adopted by the European Community in 1992 as a response to the Berne Convention. The E ...

, an additional assessment and a biodiversity management plan are required before the EBRD actually provides the approved funds. The documents should define any mitigating or compensating activities that might be needed. Izvori Omble

The development project became controversial as

non-governmental organization A non-governmental organization (NGO) or non-governmental organisation (see spelling differences) is an organization that generally is formed independent from government. They are typically nonprofit entities, and many of them are active in h ...

s (NGOs) drew public attention to a possible threat that may arise to seven species of

bat Bats are mammals of the order Chiroptera.''cheir'', "hand" and πτερόν''pteron'', "wing". With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most ...

s. Subsequently, the NGOs alleged that the project is illegal, environmentally unsafe, financially not feasible, and technically questionable. Project legality was disputed because it is based on a 1999

environmental impact assessment Environmental Impact assessment (EIA) is the assessment of the environmental consequences of a plan, policy, program, or actual projects prior to the decision to move forward with the proposed action. In this context, the term "environmental imp ...

(EIA), while Croatian legislation requires that EIAs must not be more than two years old. Flooding of Vilina Cave is cited as an environmental concern, while the financial issues are based on previous

cost overrun A cost overrun, also known as a cost increase or budget overrun, involves unexpected incurred costs. When these costs are in excess of budgeted amounts due to a value engineering underestimation of the actual cost during budgeting, they are known ...

s by

Hrvatska elektroprivreda Hrvatska elektroprivreda (HEP Group) is a national power company in Croatia which has been engaged in electricity production, transmission and distribution for more than one century, and with heat supply and gas distribution for the past few dec ...

—the state-owned company planning the development—in other projects. One objection to the technical aspects of the project is the possibility that the groundwater may trigger earthquakes. Opponents of the project have urged the

Prime Minister of Croatia , type = Head of Government , member_of = , reports_to = Croatian Parliament , appointer = Croatian Parliament , nominator = President of Croatia , termlength = At the pleasure of the parliamentary majority. Parliamentary elections must be h ...

to cancel development of the plant. After the elections of 2011,

Mirela Holy Mirela Holy (born 15 December 1971) is a Croatian politician and a former leader of the centre-left Croatian Sustainable Development, Croatian Sustainable Development party (ORaH). She served as Croatia's Minister of Environment from 2011 until ...

, who had declared her opposition to the project prior to the elections, was appointed Minister of Environment and Nature Protection. In 2012 the ministry commissioned four reviews of the EIA. The reviews—one of them supporting the EIA and three disproving the conclusions of the original EIA—were submitted to the

Government of Croatia The Government of Croatia ( hr, Vlada Hrvatske), formally the Government of the Republic of Croatia ( hr, Vlada Republike Hrvatske), commonly abbreviated to Croatian Government ( hr, hrvatska Vlada), is the main executive branch of government ...

one day after Holy resigned her post, reportedly over an unrelated matter, on 7 June 2012. Objections were raised by authors of the EIA that the reviews were not published and the names of the authors have been kept secret. Prime Minister

Zoran Milanović Zoran Milanović (; born 30 October 1966) is a Croatian politician serving as President of Croatia since 19 February 2020. Prior to assuming the presidency, he was prime minister from 2011 to 2016 and president of the Social Democratic Party f ...

said he wanted to collect opinions from the foremost Croatian, European, and worldwide experts before deciding on the matter, which has been under consideration since the early 1990s. In May 2013, the

cancelled its proposed loan to the project, pointing at environmental concerns.Victory for civil society as EBRD cancels loan for controversial Croatian dam
Bankwatch blog, May 28, 2013.

Etymology

classical antiquity Classical antiquity (also the classical era, classical period or classical age) is the period of cultural history between the 8th century BC and the 5th century AD centred on the Mediterranean Sea, comprising the interlocking civilizations of ...

, the Ombla was a part of the river Arion, rising and sinking in present-day region of

Herzegovina Herzegovina ( or ; sh-Latn-Cyrl, Hercegovina, separator=" / ", Херцеговина, ) is the southern and smaller of two main geographical region of Bosnia and Herzegovina, the other being Bosnia. It has never had strictly defined geogra ...

before resurfacing at the coast. This is the earliest known name of the river, reported in

Periplus of Pseudo-Scylax The ''Periplus of Pseudo-Scylax'' is an ancient Greek periplus (περίπλους ''períplous'', 'circumnavigation') describing the sea route around the Mediterranean and Black Sea. It probably dates from the mid-4th century BC, specifically t ...

. The most likely etymology of the river's name is that it is derived from the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

''Vimbula'', being named after vineyards, or ''Humbla'', since the river was once in

Zachlumia Zachlumia or Zachumlia ( sh-Latn-Cyrl, separator=" / ", Zahumlje, Захумље, ), also Hum, was a medieval principality located in the modern-day regions of Herzegovina and southern Dalmatia (today parts of Bosnia and Herzegovina and Croatia ...

. Alternatively it is proposed that the name of the river descended from the Slavic word ''ubao'' or ''ubla'', meaning a pit containing water, possibly a

water well A well is an excavation or structure created in the ground by digging, driving, or drilling to access liquid resources, usually water. The oldest and most common kind of well is a water well, to access groundwater in underground aquifers. Th ...

. Since the 16th century, the river was called ''Ombla'' or ''Umbla'', or a variety of similar names which all translate as "River"—''Rika'', ''Rieka'', ''Ričina'', and ''Rijeka''. In the 19th century, the use of name ''Orion'' was also reported, apparently based on the ''Arion'' of the classical period. The word ''ombla'' means 'sweet water' in Albanian.

References