channels, and three sets of locks. An additional artificial lake, Alajuela Lake (known during the American era as Madden Lake), acts as a reservoir for the canal. The layout of the canal as seen by a ship passing from the Atlantic to the Pacific is: From the formal marking line of the Atlantic Entrance, one enters Limón Bay (Bahía Limón), a large natural harbor. The entrance runs . It provides a deepwater port (Cristóbal), with facilities like multimodal cargo exchange (to and from train) and the Colón Free Trade Zone (a free port). A channel forms the approach to the locks from the Atlantic side. The Gatun Locks, a three-stage flight of locks long, lifts ships to the Gatun Lake level, some above sea level. Gatun Lake, an artificial lake formed by the building of the Gatun Dam, carries vessels across the isthmus. It is the summit canal stretch, fed by the Gatun River and emptied by basic lock operations. From the lake, the Chagres River, a natural waterway enhanced by the damming of Gatun Lake, runs about . Here the upper Chagres River feeds the high-level-canal stretch. The Culebra Cut slices through the mountain ridge, crosses the continental divide and passes under the Centennial Bridge. The single-stage Pedro Miguel Lock, which is long, is the first part of the descent with a lift of . The artificial Miraflores Lake long, and above sea level. The two-stage Miraflores Locks is long, with a total descent of at mid-tide. From the Miraflores Locks one reaches Balboa harbor, again with multimodal exchange provision (here the railway meets the shipping route again). Nearby is Panama City. From this harbor an entrance/exit channel leads to the Pacific Ocean (Gulf of Panama), from the Miraflores Locks, passing under the Bridge of the Americas. Thus, the total length of the canal is . Navigation Gatun Lake Created in 1913 by damming the Chagres River, the Gatun Lake is a key part of the Panama Canal, providing the millions of liters of water necessary to operate its locks each time a ship passes through. At time of formation, Gatun Lake was the largest human-made lake in the world. The largest island on Gatun Lake is Barro Colorado Island. It was established for scientific study when the lake was formed, and is operated by the Smithsonian Institution. Many important scientific and biological discoveries of the tropical animal and