Spillway
South of the small lock is a spillway dam with tainter gates used to regulate the freshwater levels of the ship canal and lakes. The gates on the dam release or store water to maintain the lake within a 2 ft (0.61 m) range of 20 to 22 ft (6.1 to 6.7 m) above sea level. Maintaining this lake level is necessary for floating bridges, mooring facilities, and vessel clearances under bridges.
"Smolt flumes" in the spillway help young salmon to pass safely downstream. Higher water levels are maintained in the summer to accommodate recreation as well as to allow the lakes to act as a water storage basin in anticipation of drought conditions.
Read more about this topic: Hiram M. Chittenden Locks