Blyth Valley was a local government district and borough in south-east Northumberland, England, bordering the North Sea and Tyne and Wear. The two principal towns were Blyth and Cramlington. Other population centres include Seaton Delaval, and Seaton Sluice.The borough was formed on 1 April 1974 by the merger of the borough of Blyth, Seaton Valley urban district, and part of the borough of Whitley Bay.