The Hiram M. Chittenden Locks link the fresh waters of Lake Washington and Lake Union to the east of Seattle with the salt water of Puget Sound, allowing 100 000 boats to pass this way every year under the watchful eyes of visitors on the north bank. On the south bank, a salmon ladder enables fish to make their way upstream during the spawning season. Opened in 1917, the complex includes two locks, a dam, an overflow, botanic gardens and a visitor centre.