A subterranean river is a river that runs wholly or partly beneath the ground surface – one where the riverbed does not represent the surface of the Earth (rivers flowing in gorges are not classed as subterranean). It should also not be confused with an aquifer which may flow like a river but is contained within a permeable layer of rock or other unconsolidated materials.
Subterranean rivers may be entirely natural, flowing through cave systems. In karst topography, rivers may disappear through sinkholes, continuing underground. In some cases, they may emerge into daylight further downstream. Some fish (colloquially known as cavefish) and other troglobite organisms are adapted to life in subterranean rivers and lakes. The longest subterranean river in the world is located in Mexico.
Subterranean rivers can also be the result of covering over a river and/or diverting its flow into culverts, usually as part of urban development. Reversing this process is known as daylighting a stream and is a visible form of river restoration. One successful example is the Cheonggyecheon in the centre of Seoul.
Examples of subterranean rivers also occur in mythology and literature.
There are many natural examples of subterranean rivers. Among others:
- In Bosnia and Herzegovina: Unac; Mušnica-Trebišnjica-Krupa/Ombla (Ombla springs out of huge cave near Dubrovnik, Croatia and after just cca 30 meters empties into Adriatic Sea's ria called Rijeka Dubrovačka); Zalomka-Buna/Bunica/Bregava; Vrljika-Trebižat; Lištica-Jasenica; Šuica-Ričina
- The Camuy River located in the northwestern region of Puerto Rico is one of the largest underground river systems in the world.
- The Cross Cave system in Loška Dolina, Slovenia includes 22 subterranean lakes
- The Lost River in the Appalachian Mountains of West Virginia disappears underground and reappears as the Cacapon River
- The Mojave River in southern California flows underground in most places
- The Phong Nha-Kẻ Bàng National Park in Vietnam has an underground river flowing through its cave system
- The Puerto Princesa Subterranean River on the island of Palawan, Philippines flows underground before emerging into the West Philippine Sea 
- The Punkva in Moravian Karst, Moravia, Czech Republic underground river flowing through cave system - Punkva Caves and Macocha gorge.
- The Santa Fe River in northern Florida drops into a large sinkhole in O'Leno State Park and reappears in the adjacent River Rise Preserve State Park, 3 miles (4.8 km) downstream
In many cities there are natural streams which have been partially or entirely built over. Such man-made examples of subterranean urban streams are too numerous to list, but notable examples include:
- The Bièvre underneath Paris, France
- The Fleet and other subterranean rivers of London
- The Frome underneath Bristol
- The Hobart Rivulet in Tasmania
- Mill Creek in Philadelphia
- The Neglinnaya River, which runs through a series of tunnels underneath the central part of Moscow
- The Tank Stream underneath Sydney, Australia
- The River Team underneath the Team Valley Trading Estate, Gateshead, United Kingdom
- The Zenne underneath Brussels, following the covering of the Zenne between 1865 and 1871
- Castle Frank Brook, Garrison Creek, Russell Creek, and Taddle Creek, and other subterranean urban streams in Toronto
- The Park River underneath Hartford
Mythology and literature
Greek mythology included the Styx, Phlegethon, Acheron, Cocytus, and Lethe as rivers within the Underworld. Dante Alighieri, in his Inferno, included the Acheron, Phlegethon, and Styx as rivers within his subterranean Hell. The river Alph, running "Through caverns measureless to man / Down to a sunless sea" is central to the poem Kubla Khan, by Samuel Taylor Coleridge.
"Hans was not mistaken," he said. "What you hear is the rushing of a torrent."
"A torrent?" I exclaimed.
"There can be no doubt; a subterranean river is flowing around us."
Several other novels also feature subterranean rivers. The subterranean rivers of London feature in e.g. the novel Drowning Man by Michael Robotham as well as in the novel Thrones, Dominations by Dorothy L. Sayers and Jill Paton Walsh in which a character remarks:
"You can bury them deep under, sir; you can bind them in tunnels, ... but in the end where a river has been, a river will always be."
- Hamza River
- Abîme – A vertical shaft in karst terrain that may be very deep and usually opens into a network of subterranean passages
- Karst – Topography formed from the dissolution of soluble rocks
- Losing stream
- Speleology – Science of cave and karst systems
- Subterranean rivers of London
- Subterranean rivers in Hong Kong
- Subterranean waterfall
- Underground lake
|Wikimedia Commons has media related to Underground rivers and lakes.|
- William Herbert Hobbs, Earth Features and Their Meaning: An Introduction to Geology for the Student and the General Reader, Macmillan, 1912, pages 182 and 189.
- William B. White and David C. Culver (eds), Encyclopedia of Caves, 2nd ed, Academic Press, 2012, ISBN 0123838339, p. 468.
- Richard J. Heggen: Underground Rivers from the River Styx to the Rio San Buenaventura with Occasional Diversions, University of New Mexico.
- Revkin, Andrew C. (16 July 2009). "Rolling Back Pavement to Expose Watery Havens". New York Times. Retrieved 16 March 2010.
- Kirk, Donald (2005-10-13). "Seoul peels back concrete to let a river run freely once again". World>Asia Pacific. The Christian Science Monitor. Retrieved 2006-08-21.
- "Devon Karst: Karst of the Dinaric Alps - the Dinarides in Bosnia and Herzegovina". devonkarst.org.uk. Retrieved 5 July 2018.
- "Devon Karst: Gatačko Polje - GP-Ponor Dobrelji". devonkarst.org.uk. Retrieved 5 July 2018.
- "Parque de las Cavernas del Río Camuy - Video Guide - Camuy, Puerto Rico - EyeTour.com". places.eyetour.com.
- "Administrative Order No. 29, s. 2012 - GOVPH". officialgazette.gov.ph.
- Jules Verne, A Journey to the Center of the Earth, translated by Frederick Amadeus Malleson, 1877, at Project Gutenberg.
- Dorothy L. Sayers and Jill Paton Walsh, Thrones, Dominations, Hodder and Stoughton, 1998, p. 313.