Alviela River (, ) is a

river A river is a natural stream of fresh water that flows on land or inside Subterranean river, caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of ...

Portugal Portugal, officially the Portuguese Republic, is a country on the Iberian Peninsula in Southwestern Europe. Featuring Cabo da Roca, the westernmost point in continental Europe, Portugal borders Spain to its north and east, with which it share ...

. It is long. The Alviela spring is one of the deepest in the world and is locally connected to a cave complex that represents the most significant fluvio-karstic phenomena in Portugal, one which supports several bat colonies with more than 5,000 bats in total. In 2007, a population of

troglomorphic Troglomorphism is the morphological adaptation of an animal to living in the constant darkness of caves, characterised by features such as loss of pigment, reduced eyesight or blindness, and frequently with attenuated bodies or appendages. The ter ...

Procambarus clarkii ''Procambarus clarkii'', known variously as the red swamp crayfish, Louisiana crawfish or mudbug, is a species of cambarid crayfish native to freshwater bodies of northern Mexico, and southern and southeastern United States, but also introduc ...

'', an invasive

crayfish Crayfish are freshwater crustaceans belonging to the infraorder Astacidea, which also contains lobsters. Taxonomically, they are members of the superfamilies Astacoidea and Parastacoidea. They breathe through feather-like gills. Some spe ...

species, was recorded in the Alviela spring, raising concerns about their potential effect on native

stygobitic Stygofauna are any fauna that live in groundwater systems or aquifers, such as caves, fissures and vugs. Stygofauna and troglofauna are the two types of subterranean fauna (based on life-history). Both are associated with subterranean environment ...

fauna. These crayfish lack all body pigment, although pigmented specimens were recorded in nearby surface waters. The river has its origin in a

karst spring A karst spring or karstic spring is a Spring (hydrology), spring (exsurgence, 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 i ...

. Ribeira dos Amiais, 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 ...

, infiltrates through the Sumidouro da Ribeira dos Amiais, a

ponor A ponor is a natural opening where surface water enters into underground passages; they may be found in Karst topography, karst landscapes where the geology and the geomorphology is typically dominated by porous limestone rock. Ponors can drain s ...

, only to return to the surface 250 m further on through a

canyon A canyon (; archaic British English spelling: ''cañon''), gorge or chasm, is a deep cleft between escarpments or cliffs resulting from weathering and the erosive activity of a river over geologic time scales. Rivers have a natural tendency t ...

. Nascente do Alviela.JPG, Ribeira dos Amiais, tributary of Alviela Sumidouro da Ribeira dos Amiais - Portugal (26498565342).jpg, Sumidouro da ribeira dos Amiais, were the water from the stream infiltrates

References

Rivers of Portugal {{Portugal-river-stub