Today I saw a  Ring-necked Duck on a pond by Þingvallavatn Lake. This was an adult male in a group of Tufted Ducks. Ring-necked Ducks are annual vagrants in Iceland and usually the visitors are males. Sometimes they mate with Tufted Duck females and once in a while you see hybrids of these species.
Ring-necked Ducks are North American and there they are common on woodland ponds.