Nearly 500 rivers lace Panama's rugged landscape. Mostly unnavigable, many originate as swift highland streams, meander in valleys, and form coastal deltas. However, the Río Chagres (Rio Chagres) is one of the few wide rivers and a source of enormous hydroelectric power. The river is located in central Panama. The central part of the river is dammed by the Gatun Dam and forms Gatun Lake, an artificial lake that constitutes part of the Panama Canal. The lake was created between 1907 and 1913 by the building of the Gatun Dam across the Chagres River. At the time it was created, Gatun Lake was the largest man-made lake in the world, and the dam was the largest earth dam. It drains northwest into the Caribbean. The Kampia and Madden Lakes (also filled with water from the Río Chagres) provide hydroelectricity for the area of the former Canal Zone. The Río Chepo, another source of hydroelectric power, is one of the more than 300 rivers emptying into the Pacific. These Pacific-oriented rivers are longer and slower running than those of the Caribbean side. Their basins are also more extensive. One of the longest is the Río Tuira which flows into the Golfo de San Miguel and is the nation's only river navigable by larger vessels.