Kathmandu is dissected by eight rivers, the main river of the valley, the Bagmati and its tributaries, of which the Bishnumati, Dhobi Khola, Manohara Khola, Hanumant Khola, and Tukucha Khola are predominant. The mountains from where these rivers originate are in the elevation range of 1,500–3,000 metres (4,900–9,800 ft), and have passes which provide access to and from Kathmandu and its valley. An ancient canal once flowed from Nagarjuna hill through Balaju to Kathmandu; this canal is now extinct.