A known site of high archaeological importance is the former Hackensall Tide Mill (Site PRN15022, SD 35114659) at Preesall. This mill is known from documentary sources and may date from before 1260; its site is indicated on the OS 1:10,560 mapping of 1848 (sheet Lancashire 43). Other watermill sites of this period are known in the county, although this appears to be the only tide mill and very few simple medieval mill sites have been investigated in the field. Physical remains of medieval watermills are rare nationally and surviving remains are likely to be of national, rather than local, importance.