The Runcorn Railway Bridge, Ethelfleda Bridge or Britannia Bridge crosses the River Mersey at Runcorn Gap between Runcorn and Widnes in Cheshire, England. It is alongside the Silver Jubilee Bridge. The bridge is recorded in the National Heritage List for England as a Grade II* Listed building.

The River Mersey is a major river in North West England. Its name derives from Old English and means "boundary river", possibly referring to its having been a border between the ancient kingdoms of Mercia and Northumbria. For centuries it has formed part of the boundary between the historic counties of Lancashire and Cheshire.