A water mass identified and named by Stef´ansson (1968). It is homogenised in winter north of Iceland from a mixture of Modified North Atlantic Water (MNAW) from the North Icelandic Irminger Current and water from the near–surface layers of the Iceland Sea plus some coastal water influenced by runoff. The typical properties of NIWW are a temperature from 2–3°C and a salinity of 34.85–34.90.