It is about 19 km long, with an average width of 9–16 m. It springs from the cave at a height of 325 m above sea level, below the high cliff of Kičej hill (606 m above sea level). Until 1870 the river's spring was below the next hill, Podjavorje, but it collapsed in an earthquake near the village of Klana. The most noticeable confluents are Sušica, Lužac, Zala, Zahumčica, Golubinka, Ričinica and Borovšćica, but they are dry for most of the year. In 1968 a dam was built to facilitate a hydroelectric power plant, creating lake Valići but destroying the village of the same name. Rječina flows through the canyon for almost half of her length. In Rijeka, the river branches into two parts: Mrtvi canal (the old basin), and the new canal, which was built in the 19th century when Mrtvi canal was used as a harbour. The most well-known sight is Gaspar's watermill (Gašparov mlin) in Martinovo Selo which was renewed in the 90s. Notable fauna are trout and river crabs.
This river has often been the border between different states. The first time this happened was from the 13th to 16th centuries when it formed the border between the Lands of the Crown of Saint Stephen and the Habsburgs. A similar thing happened in 1868 when Rječina became the border between the Croatian and Hungarian parts of Austro-Hungary. After World War I it became for a very short time the border between the Free State of Fiume and the Kingdom of the Serbs, Croats and Slovenes. After the Free State of Fiume was annexed by Italy, Rječina became the border river of that country. After World War II Rječina was no longer a border between states.