The city of Rijeka is named after the river Rječina. The river is the most significant watercourse of the Croatian coast, and is rich in a number of tributaries such as Sušica which is also the largest left tributary, Lužac, Zala, Zahumčica, Golubinka, Ricinica, Borovščica. The river has a karst spring and its water flows from the karst cave. It has two very important roles, namely water supply and electricity generation. Mrtvi kanal is the oldest natural port in Rijeka, where the traffic of ships took place even after the artificial port in Rijeka was built. When talking about economic activity, one must also mention the old Gašpar mill in Martin's village. In 1985, the area of the Rječina Canyon was designated protection, ensuring the survival of many plants and animals. Research to date has identified new habitats for evergreen species, as well as wildlife such as aquatic invertebrates, trout and white-clawed crayfish. Besides pollution, the threats are riverbed sedimentation, the destruction of the natural dam and the propagation of the water wave all the way to the mouth. There is also another danger of landsliding near the river bed, which can lead to flooding. Planning document from the Municipality of Jelenje provides examples of ecosystem protection such as municipal waste management, construction of sewage system and collection of rainwater.