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The Hiram M. Chittenden Locks are a complex of locks that sit in the middle of Salmon Bay,[citation needed] part of Seattle's Lake Washington Ship Canal.[2] They are known locally as the Ballard Locks[3][4] after the neighborhood to their north. (Magnolia lies to the south.)[citation needed]..The locks and associated facilities serve three purposes:..    * To maintain the water level of the fresh water Lake Washington and Lake Union at 20?22 feet above sea level[2][3] (Puget Sound's mean low tide).[citation needed].    * To prevent the mixing of sea water from Puget Sound with the fresh water of the lakes (saltwater intrusion).[5].    * To move boats from the water level of the lakes to the water level of Puget Sound, and vice versa.[6]..The complex includes two locks, a small (30 x 150 foot, 8.5 x 45.7 meter) and a large (80 x 825 foot, 24.4 x 251.5 meter).[7] The complex also includes a (235 foot, 71.6 meter) spillway with six (32 x 12 foot, 9.8 x 3.7 meter) gates to assist in water-level control.[7] A fish ladder is integrated into the locks for migration of anadromous fish, notably salmon.[8][6]..The grounds feature a visitors center,[9] as well as the Carl S. English, Jr., Botanical Gardens.[10]..Operated by the U.S. Army Corps of Engineers,[11] the locks were formally opened on July 4, 1917,[12] although the first ship passed on August 3, 1916.[13]They were named after U.S. Army Major Hiram Martin Chittenden, the Seattle District Engineer for the Corps of Engineers from April 1906 to September 1908.[9] They were added to the National Register of Historic Places in 1978.[1]