Mystic River Railroad Bridge, Railway swing bridge in Mystic, Connecticut, US.

The Mystic River Railroad Bridge is a steel truss structure carrying two tracks of the Amtrak Northeast Corridor across the Mystic River between Groton and Stonington townships. The structure can open to allow ships to pass, creating a functional meeting point between rail and water traffic.

The current structure was built in 1984 and replaced a steel swing bridge from 1875, which in turn had succeeded an original wooden drawbridge from 1819. This progression reflects how infrastructure repeatedly adapted to the demands of evolving transportation.

The bridge carries Amtrak's Northeast Regional and Acela Express trains, and Shore Line East has been proposed to extend from New London to Mystic, which would mean crossing it. The Historic American Engineering Record documents the structure as CT-26, with 14 photographs and 10 data pages.

The bridge sits between Groton and Stonington, where the Mystic River meets the Northeast Corridor; riverside spots and nearby roads give views of the truss and its swing span. When closed it leaves only 13 feet (4.0 m) of vertical clearance, so small craft pass beneath without an opening.

The structure holds the distinction of being the easternmost movable bridge on Amtrak's Northeast Corridor section within Connecticut. This boundary status makes it a notable marker between two different infrastructure networks.