Nepal has three categories of rivers. The largest systems -— from east to west the Koshi, Gandaki/Narayani, Karnali/Goghra and Mahakali—originate in multiple tributaries rising in or beyond the high Himalaya that maintain substantial flows from snowmelt through the hot, drought-stricken spring before the summer monsoon. These tributaries cross the highest mountains in deep gorges, flow south through the Middle Hills, then join in candelabra-like configuration before crossing the Lower Himalayan Range and emerging onto the plains where they have deposited megafans exceeding in area.