There are 103 rivers/streams with most flowing from the lovely mountains of SriLanka. The longest by far is the Mahaweli. It starts its 333 km journey near Adam's Peak and winds its way into the Indian Ocean at Koddiyar Bay near Trincomalee.   Other major rivers include the following... Malwathu Oya 165 km Kelaniya River 145 km Yan Oya 142 km Walawe River 137 km Kalu Ganga 129 km Maha Oya 134 km The only major river that does not begin in the highlands is the 148 km long Kala - Oya. Its source is the gigantic Kalawewa Reservoir built in the 5th Century. Most of the rivers are navigatable for most of their length by boats that have a shallow draft.