difficulties on different rivers. The ratings usually are various from 1 to 5 stars, even though a few rivers can be more than five stars because of their extreme difficulties. Such ratings are largely subjective, depending largely on river trekker's own experience. Therefore, different people or hiking groups would give different number of stars on the same river. According to Hong Kong Adventurer, an English Website about hiking and river trekking in Hong Kong, difficult scale of different rivers as: Risks and dangers River trekking has a certain level of risk. There are occasional accidents in river trekking, including falls from steep cliffs or waterfalls, drownings, exhaustion, or getting lost. Risks that should be prepared for include the following: Flash flooding poses a serious danger. Sudden changes in weather, like rainstorms, can cause rapid rises in the level and speed of the river water. Also, the number of viable paths and climbing areas inside the river valley could be reduced suddenly in a very short period. Visibility can be limited by rainy or misty weather. Low visibility may come in too quickly for trekkers to adapt to. Therefore, a torch (flashlight), preferably a head-mounted one, is a must for river trekking. Steep cliffs inside river valleys require a certain level of rock-climbing skills. However, because of the humid environment inside river valleys, some rock surfaces can be wet and some rocks may be loose despite appearing solid. To deal with wet climbing conditions, professional river-trekking boots are strongly advised. See also Canyoning Hiking Kloofing Geography of Hong Kong Country parks and conservation in Hong Kong Environment of Hong Kong References and external links Sport in Hong Kong ja:沢登り zh:溯溪