The Mersey Barrage is a proposed scheme for building a tidal barrage across the Mersey Estuary. In December 2022, the Liverpool City Region mayor announced cooperation between the City Region and K-water of South Korea, who built and operates the Sihwa Lake Tidal Power Station, in order to construct a similar operation on the River Mersey.

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.