Nanshi Stream 南勢溪 is one of the primary sources of the Xindian River 新店溪 which outlines the western edge of Taipei city and is central to the story of the capital. Nanshi stream (meaning “south stream”) drains the entire 332 km2 watershed of Wulai District 烏來 south of Taipei over its 45 km run.

With headwaters at Songluo Lake 松羅湖 in the mountains of Qilan 棲蘭山, Nanshi Stream flows north to Hapen 哈盆 and the botanical research and educational facility of Fushan Botanical Garden 福山植物園 before flowing west to Fushan 福山 to pick up Zhakong River 扎孔溪 and Daluolan River 大羅蘭溪 (Tranan). From Fushan, Nanshi Stream flows north through Neidong Forest Recreation Area 內洞森林遊樂區 cutting a deep gorge through shale stratum over 100 m deep before picking up its largest tributary, Tonghou Creek 桶後溪 in the scenic Atayal village of Wulai 烏來 before continuing to Guishan 龜山 where it is joined by Beishi Creek 北勢溪 flowing out of the Feicui Reservoir 翡翠水庫 to become the Xindian river 新店溪.

Nanshi Stream flows through the 7,759 hectare Chatianshan Nature Reserve 插天山自然保留區. The Preserve, fed by a rich network of clean streams draining steep densely forested valleys is recognized as one of the most diverse reservoirs of flora and fauna on the island offering a protected habitat for endangered species, including 23 species of mammals, 72 species of birds and 14 species of amphibians, including the tawny fish owl 黃魚鴞 Ketupa flavipes, brown wood owl 褐林鴞 Strix leptogrammica, crab-eating mongoose 食蟹獴 Herpestes urva. Tonro Ginger 屯鹿月桃 Alpinia tonrokuensis is an endemic shell ginger of the area.