In Breton folklore, Iannic-ann-ôd or Yannig an Aod (in Breton ˈjãniɡ ən ˈoːt/; meaning "Little John of the shore"), are said to be the lost souls of those drowned at sea and were never recovered. They are said to be heard along coastlines at night crying, "Iou! Iou!".
From The Celtic Legend of the Beyond: