Wallasey Pool was a natural tidal inlet of water that separated the towns of Wallasey and Birkenhead on the Wirral Peninsula, England. Originally flowing directly into the River Mersey, it was converted into the sophisticated Birkenhead Dock system from the 1820s onwards by land reclamation, with the main portion of the pool becoming known as the Great Float. In 1933, with the exception of a small lake, the head of Wallasey Pool at Poulton was converted into Bidston Dock.