Canal Lake Arch Bridge
Completed in 1905, this noteworthy structure on the Trent-Severn Waterway is the earliest-known reinforced concrete bridge in Canada. It was built using the Melan system of reinforcement with curved steel girders to reduce the amount of concrete required, resulting in a comparatively slender arch. This structure illustrates the transition from stone to concrete, with massive abutments and surface markings imitative of its masonry predecessors. A precursor of large-span reinforced concrete bridges, the Arch Bridge is an important milestone in the history of civil engineering in Canada.
Plaque via Alan L. Brown's site Ontario Plaques. Full page here.