Thi Lo Su Waterfall is one main reason people travel to Umphang. It is the largest waterfall of Thailand, containing many smaller drops combined together for a magnificent view. Its height is about 200 meters and total width is about 400 meters. It is most beautiful during rainy season from June to November because of the larger water flow. However, during this period, the road access to the waterfall is closed for safety reason and some hiking is required. The peak season for tourism is in December and January where the water level is still high and the road to waterfall (25 km) is open for public. Only cars with four wheel drive can pass this steep and slipperly road. An alternative way to reach the waterfall is by whitewater rafting downstream along the calm section of Klong River and then continue journey either on foot or by car for another about 12 km. Travelling this way, two waterfalls dropping into Klong River will be seen: Thi Lo Jo Waterfall (น้ำตกทีลอจ่อ), and Sai Rung Waterfall (น้ำตกสายรุ้ง). The name Thi Lo Su, in Karen language, means giant waterfall or black waterfall.