Navy Island is the only Canadian island in the Niagara River. The 127.9 ha island is named after a British shipyard (1793) where the first naval vessels to sail the Upper Great Lakes were constructed. During the Rebellions of 1837-38, William Lyon Mackenzie here proclaimed his short-lived republic of Upper Canada. Partially cleared for farming in the mid-1850s, a summer resort hotel (1876) survived until the 1910s.

The island is federal crown land but has been controlled by the Niagara Parks Commission since 1938. It was proposed as the site for a permanent United Nations headquarters in 1945 and then considered for a potential new highway route from the US across Grand Island to the Queen Elizabeth Way. Declared a wildlife and crown preserve in 1949, it is now rarely visited except for limited summer camping under permit. Access is solely by boat.