Luda Kamchiya (Bulgarian: Луда Камчия [ˈɫudɐ ˈkamt͡ʃijɐ], lit. 'Mad Kamchiya') is a river in eastern Bulgaria, the main tributary of the Kamchiya river. The river has a total length of 180 km and a drainage basin of 1610 km², with an average slope of 5.3‰. Luda Kamchiya rises from the Balkan Mountains in the area of Sliven, then flows between two arms of the mountains before crossing through the Luda Kamchiya Gorge and flowing into northern Bulgaria, joining Golyama Kamchiya near Dalgopol to form the Kamchiya river.