The Merrow, from Ireland, seem to be more closely related to the traditional depiction of Merpeople, both in Harry Potter,1 and in folklore.2
Harry Potter Wiki "Merrow" Last Edited: 2021-08-04. Last Viewed: 2021-11-11. ↩
Wikipedia "Merrow" Last Edited: 2021-07-16. Last Viewed: 2021-11-11 ↩