The Panama Canal is a lock and lake canal, crossing the Isthmus of Panama from the Caribbean Sea in a southeasterly direction to the Bay of Panama of the Pacific Ocean. It is 50 miles long from deep water to deep water, at least 500 feet wide at the bottom of excavated channels, 110 feet wide in look chambers, which have a usable length of 1000 feet. Depth varies but is not less than 40 feet. Average time in transit is 12 hours. Gatun Dam blocks the Chagres river near its Atlantic mouth, creating Gatun Lake, 23 3/4 miles long, 85 feet above sea level, about 45 feet deep. Ships ascend to the lake by locks and then pass through Gaillard Cut, 8 miles long.