It faces Liverpool over the River Mersey to the east , the Irish Sea to the north and the River Dee to the west . The city of Liverpool over the Mersey , faces the northeastern side of the Wirral . Bordering is the River Mersey to the east , the Irish Sea to the north and the River Dee to the west ; the borough of Cheshire West and Chester occupies the remainder of the Wirral Peninsula and borders the Wirral borough to the south .