The Red-necked Grebe is a waterbird that lives in temperate areas in the Northern hemisphere. It a rare vagrant in Iceland.  It breeds in fresh water lakes but winters by the coast or in estuaries.  This Red-necked Grebe was in the harbour at Þorlákshöfn in March. It is in its winter plumage which is less colourful than in summer.
See: https://www.allaboutbirds.org/guide/Red-necked_Grebe/id#