A subterranean river in the
. (Scale shown by people in photograph.)
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. It is distinct from an aquifer, which may flow like a river but is contained within a permeable layer of rock or other unconsolidated materials. A river flowing below ground level in an open gorge is not classed as subterranean. 
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. The longest subterranean river in the world is the Sistema Sac Actun cave system in Mexico. 
Subterranean rivers can also be the result of covering over a river 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.  
Some fish (colloquially known as
cavefish) and other troglobite organisms are adapted to life in subterranean rivers and lakes. 
Examples of subterranean rivers
also occur in mythology and literature.
The cave of
source of the Buna
can be entered by boat and dived through a cave system serving as an effluence of the
Devil's Throat Cave subterranean river from above
There are many natural examples of subterranean rivers. Among others:
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:
Bièvre underneath Paris, France The
Boyanska reka ( Boyana river), partially underneath Sofia, Bulgaria 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 The River Farset, which Belfast is named after, which runs in tunnels underneath the city.
Some fish (popularly known as
cavefish) and other troglobite organisms are adapted to life in subterranean rivers and lakes.
Mythology and literature
Greek mythology included the
Styx, Phlegethon, Acheron, Cocytus, and Lethe as rivers within the Underworld. Dante Alighieri, in his , included the Acheron, Phlegethon, and Styx as rivers within his subterranean Inferno 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.
The characters in
Jules Verne's encounter a subterranean river:
A Journey to the Centre of the Earth
"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 by Thrones, Dominations 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."
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.
^ "Underwater cave is the world's biggest", Mexico Daily News, January 15, 2018,
^ a b Richard J. Heggen:
, University of New Mexico. Underground Rivers from the River Styx to the Rio San Buenaventura with Occasional Diversions
Revkin, Andrew C. (16 July 2009). "Rolling Back Pavement to Expose Watery Havens". New York Times . Retrieved 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 .
^ William B. White and David C. Culver (eds),
Encyclopedia of Caves, 2nd ed, Academic Press, 2012, ISBN 0123838339, p. 468.
"Devon Karst: Karst of the Dinaric Alps - the Dinarides in Bosnia and Herzegovina". devonkarst.org.uk . Retrieved 2018.
"Devon Karst: Gata?ko Polje - GP-Ponor Dobrelji". devonkarst.org.uk . Retrieved 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, , translated by Frederick Amadeus Malleson, 1877, A Journey to the Center of the Earth at Project Gutenberg.
Dorothy L. Sayers and Jill Paton Walsh, , Hodder and Stoughton, 1998, p. 313. Thrones, Dominations