Telmatobius macrostomus, also known as the Lake Junin (giant) frog or Andes smooth frog, is a very large and endangered species of frog in the family Telmatobiidae. This completely aquatic frog is endemic to lakes and associated waters at altitudes of in the Andes of Junín and Pasco in central Peru. It has been introduced to slow-moving parts of the upper Mantaro River, although it is unclear if this population still persists. Together with the closely related Amable Maria frog (T. brachydactylus), it is sometimes placed in the genus Batrachophrynus. Ecology and appearance T. macrostomus is completely aquatic, and restricted to lakes (notably Lake Junín) and waters that are directly connected to them like rivers, streams and canals. It has also been introduced to the upper part of the Mantaro River, but it is unclear if this population persists. It is found both in large marshy lakes and smaller deep lakes. This smooth-skinned, dark brownish frog generally ranges from shallow water to a depth of , but prefers places with extensive aquatic vegetation and deep. In its native habitat the water temperature typically is between . Captives have been kept in aquariums for more than 5 years at around . It feeds on aquatic snails (especially Physidae), amphipods, aquatic insects (especially Baetidae mayfly larvae) and small fish. T. macrostomus is among the largest frogs in the world and the largest exclusively aquatic frog, a title sometimes incorrectly awarded to its somewhat smaller relative, the Titicaca water frog (T. culeus). T. macrostomus measures up to in snout–to–vent length, and in outstretched length. It can weigh up to about , and the hindlegs alone can surpass in length. Very large individuals are rare; most adults have a snout–to–vent length of and weigh less than . Females grow larger than males. The tadpoles also grow very large, up to about in length. Conservation and threats Once common, this frog is now rare and considered endangered by the IUCN. During a survey in 2012 it was only found at about 10% of the visited sites and in low densities, leading to the suggestion of recognizing it as critically endangered. The primary threats to the species are capture for human consumption, predation by introduced trout, pollution from mining, agriculture and human waste, and water fluctuations caused by the Upamayo Dam. These factors have also contributed to the decline of the native Orestias pupfish, historically an