Dingesmere is a place known only from the Old English poem of the Battle of Brunanburh. The name is found in versions of the Anglo-Saxon Chronicle from the year 937.
One of the locations that has been cited is situated on the Dee Estuary at Heswall, Wirral. Another possible location is Lingham, on the Irish Sea coastline of Wirral at Moreton.
References
Dingesmere Wikipedia(Text) CC BY-SA