The damming of the Periyar River at Thekkady, in 1895 resulted in the creation of the huge (26 sq km) Periyar lake. This is now the nucleus of the Periyar wildlife sanctuary, a rare example of human intervention having enhanced an ecosystem. Mirror still lagoons, grassy plains and naked hills, make up the landscape of Periyar, providing the perfect foil to the wildlife found there elephants, Indian bison and the endangered lion-tailed macaque. Periyar was declared a Tiger Reserve in 1978.