Río Medellín: geography

The Medellín River (Río Medellín in Spanish), called Porce River during most of its course, is a river that flows though the Colombian city of Medellín and its metropolitan area.
For many years an organization called Mi Rio (My River) was involved in cleaning the river, trying to bring the river back to its prior glory and cleanliness.
For the river's first 60 km (37 mi), it is referred to as the Medellín and the Porce thereafter. It is a tributary of the Nechi River which flows in turn into the Cauca River.

from Wikipedia