In 1960, the Thornbury fish ladder was added to the Thornbury dam to help fish get up and down stream. The fish ladder was the first fish ladder built in Ontario and took $320,000 to build. The fish ladder, also known as a fish lock, works the same way as the hydraulic boat locks found throughout the Great Lakes. This system allows fish to bypass the 7.3 metre high dam and allows them to safely travel to suitable spawning areas upstream.
Rainbow Trout are the most common fish that use this fish lock because of the 20,000 Rainbow Trout eggs they planted in the Sydenham River in the early 1900s. Mature Rainbow Trout make it down stream after they lay their eggs in early spring. They then make their way to Georgian Bay where they spend the summer. In the fall, many fish make their way back upstream to spend the winter.It is very important that the fish ladder was built because physical barriers such as falls and dams can prevent adult Rainbow Trout from spawning in proper areas. With the installation of the Thornbury Fish Ladder, the Rainbow Trout in this area have over 64 kilometres of viable water. This increase in spawning area will result in greater numbers of trout in the area to provide opportunities for recreational fishing and viewing.