The Acarai Mountains (also, Akarai Mountains) is a mountain range in the southern part of the Tigri Area on the border with Brazil. The Tigri area is a disputed territory of Guyana and Suriname. The Acarai Mountains are a wet, forested highland region of low mountains and is one of four mountain ranges in Guyana, the others being the Imataka, Kanuku and Pakaraima mountains. The headwaters of the Essequibo River, the longest river in Guyana, and the Courantyne River, have their sources in this range. The actual source of the Essequibo was discovered in 2013 by a Guyanese-German team. The mountain range was first mentioned in 1821 by A.H. Brué as Sierra do Acaray. This range is home to a single village of Wai-Wais, the descendants of surviving tribes that were once believed extinct. The village was first mentioned around 1837. The unnamed high point of this range is located at 1.36667°N, -59.18333°W, and has an altitude of 1009 m. This range extends to the east, where it becomes the Tumuk Humak Mountains along the border of Suriname and French Guiana with Brazil.