The Thysville Caves are a cave

Cave

A cave or cavern is a natural underground space large enough for a human to enter. The term applies to natural cavities some part of which is in total darkness. The word cave also includes smaller spaces like rock shelters, sea caves, and grottos.Speleology is the science of exploration and study...

 complex in the Democratic Republic of the Congo

Democratic Republic of the Congo

The Democratic Republic of the Congo is a state located in Central Africa. It is the second largest country in Africa by area and the eleventh largest in the world...

, located near the town of Mbanza-Ngungu

Mbanza-Ngungu

Mbanza-Ngungu, formerly known as Thysville or Thysstad, named after Albert Thys, is a city in Bas-Congo Province in the western part of the Democratic Republic of Congo, lying on a short branch off the Matadi-Kinshasa Railway...

 (formerly Thysville). The cave complex is fed by tributaries of the Lower Congo River

Congo River

The Congo River is a river in Africa, and is the deepest river in the world, with measured depths in excess of . It is the second largest river in the world by volume of water discharged, though it has only one-fifth the volume of the world's largest river, the Amazon...

, and extends across an area of 750 square kilometers.

Flowing water carries nutrients from the surface into the caves, which nourishes aquatic life adapted to the lightless environment. The caves are home to an endemic

Endemic (ecology)

Endemism is the ecological state of being unique to a defined geographic location, such as an island, nation or other defined zone, or habitat type; organisms that are indigenous to a place are not endemic to it if they are also found elsewhere. For example, all species of lemur are endemic to the...

 blind cyprinid

Cyprinid

The family Cyprinidae, from the Ancient Greek kyprînos , consists of the carps, the true minnows, and their relatives . Commonly called the carp family or the minnow family, its members are also known as cyprinids...

 fish, Caecobarbus geertsii, listed as endangered in the IUCN Red List

IUCN Red List

The IUCN Red List of Threatened Species , founded in 1963, is the world's most comprehensive inventory of the global conservation status of biological species. The International Union for Conservation of Nature is the world's main authority on the conservation status of species...

. The caves are relatively unknown scientifically, and may be home to other endemic fish and invertebrate species.