The river's three tributaries are the Xindian River, Dahan River and Keelung River. The Dahan River is the main tributary and has its headwaters in the Pintian Mountain in Hsinchu County and flows through Hsinchu County, Taoyuan City and New Taipei City. As a river system including the Dahan River, the Tamsui River has a total length of and a drainage area of .