River traffic is important on the Si, although navigation is obstructed at many points by rapids and shallows. Ships of 10,000 tons call at Whampoa, Canton’s outer port, and vessels of 9-foot draft can travel upriver to Wuchow, the limit for ocean-going ships. Junks reach far into Kwangsi, and the Yuh is navigable for many months right up to Poseh on the Yunnan border, in spite of the difficult rapids between Kweiping and Nanning.