Most American rivers were made unnavigable by rapids and waterfalls. Mostly unnavigable, many originate as swift highland streams, meander in valleys, and form coastal deltas. The narrowest point is in the headwaters, an unnavigable marsh in Indian River County. The dam will submerge over 300 shoals, which had rendered the upper Hongshui unnavigable. Over the centuries sand and silt deposits made the port unnavigable. Any damage to the canal bank could thus render the entire canal unnavigable. Some intermediate reaches are unnavigable and by-passed by canals. Two attempts by Mike Cumberlege to make the Corinth Canal unnavigable ended in failure. This lay at the head of an inlet which was partially unnavigable at low water. Waters may be unnavigable because of ice, particularly in winter. The lake has a reputation for periodically powerful, unnavigable storms. High water speed may make a channel unnavigable. Over the years this erosion caused sedimentation, leading the Western Branch to become unnavigable. He said it was unnavigable, being filled with ice. The Nine Foot Drain, also unnavigable, meets the Slea just before Southgate.