The Křemelná river is one of two headstreams of the Otava river (the other one is the Vydra river). It springs near the town Železná Ruda on the slope of Můstek mountain 1,214 m a.s.l. The confluence with the Vydra river (and the origin of the Otava river) is near the small village Čeňkova Pila.
The length of the Křemelná river is 30 km and it takes water from the area 172 square km.
A part of the river between the confluence with the Prášilský Potok (Prášily Stream) and the small village Rejštejn is navigable for canoes.
The Vchynicko-Tetovský Kanál (Vchynice-Tetov Canal) was built for floating timber between the Křemelná and Vydra rivers in the 19th century.