From its source in the Sierra Madre Mountains, the Marikina River, which is crisscrossed by the West Valley Fault Line, flows through six of Metro Manila’s 16 cities, before it merges with the great Pasig River and eventually the sea. 

Some of its waters will be diverted through the artificially constructed Mangghan floodway (pictured) leading it to the fresh-water lake, Laguna De Bay.