Bali's central mountains include several peaks over 3,000 metres in elevation. The highest is Mount Agung (3,031 m), known as the "mother mountain" which is an active volcano. Mountains range from centre to the eastern side, with Mount Agung the easternmost peak. Bali's volcanic nature has contributed to its exceptional fertility and its tall mountain ranges provide the high rainfall that supports the highly productive agriculture sector. South of the mountains is a broad, steadily descending area where most of Bali's large rice crop is grown. The northern side of the mountains slopes more steeply to the sea and is the main coffee producing area of the island, along with rice, vegetables and cattle. The longest river, Ayung River, flows approximately 75 km.
The island is surrounded by coral reefs. Beaches in the south tend to have white sand while those in the north and west have black sand. Bali has no major waterways, although the Ho River is navigable by small sampan boats. Black sand beaches between Pasut and Klatingdukuh are being developed for tourism, but apart from the seaside temple of Tanah Lot, they are not yet used for significant tourism.
Subak irrigation system.