The Ballard Locks area is actually composed of three separate park spaces, the Carl S. English Jr Botanical Gardens, the Hiram M. Chittenden Locks, and Commodore Park. Most visitors access the locks through the botanical gardens.
After the completion of the locks in 1911, Carl English, a Landscape Architect used the abandoned 7 acre construction site to create a park in the English landscape style. He then spent over 40 years tending the garden and planting over 500 species of plants from all over the world.
The Hiram M. Chittenden Locks were named after the Seattle District Engineer from 1906-1908 and were built by the Army Corp of Engineers, who continue to maintain and operate them. The Locks were built in 1911 and officially dedicated on July 4th 1917. They are designed to serve 3 purposes. Firstly, to maintain the water levels in Lake Union and Lake Washington. Secondly, to prevent saltwater intrusion into said lakes, and thirdly, to allow boats to pass the dam. The Locks were added to the registry of National Historic Places in 1978.
In 1966 there was a plan to build apartments on the southern waterfront near the locks, and in response, a group calling themselves the Green Belt Association formed in the hopes of preserving this area as a park. Its goals were realized in 1978 when a 3.9 acre park was opened. It was named Commodore Park after the street that formed it's southern edge.
On the whole, the Locks are an interesting tourist spot. The parks tend to be empty, while the locks themselves usually have a small crowd of people. The salmon tend to run July/August so that's usually the time to visit.