The Vilyuy River (also Vilyui, Russian: Вилю́й; IPA: [vʲɪˈlʲʉj]; Sakha: Бүлүү) is a river of the Central Siberian Plateau, longest tributary of the Lena River. About 2,650 kilometres (1,650 mi) long, it flows mostly within the Sakha Republic. Its basin covers about 491,000 square kilometres (190,000 sq mi).