The mata mata, mata-mata, or matamata (Chelus fimbriata)[7] is a South American species of freshwater turtle found in the Amazon basin and river system of the eastern Guianas.

It was formerly believed to also occur in the Orinoco basin, western Guianas and upper Rio Negro–Branco system, but in 2020 these populations were found to belong to a separate species, Chelus orinocensis (Orinoco mata mata).

In 1805, it was moved to its own genus as Chelys fimbriata by André Marie Constant Duméril.

In 1963, the International Commission on Zoological Nomenclature resolved the issue of Testudo terrestris (Fermín 1765) by declaring it a nomen oblitum (meaning that only Testudo terrestris Forsskål 1775 is valid and a synonym for the Greek tortoise), while also declaring that Chelys fimbriata is a conserved name for the mata mata.

[1][10] In 1995, distinct morphological differences were found between the populations of the Amazon and Orinoco basins.

[13] The neck is longer than the vertebra under its carapace and is fringed with small skin flaps along both sides.

[13] Hatchlings show a pink to reddish tinge in the underside edge of their carapaces and plastrons that gradually disappear as they grow.

[18] As it remains motionless in the water, its skin flaps enable it to blend into the surrounding vegetation until a fish comes close.

The turtles predominantly feed at night in muddy water with limited visibility.

As with all aquatic turtles, water quality is one of the keys to keeping this species successfully in captivity.

Warm, acidic water is the best type used with a high tannin content that should be maintained all year round.