This is a list of Orkney islands in Scotland. The Orkney archipelago is located north of mainland Scotland and comprises over 70 islands and skerries, of which 20 are permanently inhabited. In addition to the Orkney Mainland there are three groups of islands. The North and South Isles lie respectively north and south of Mainland. The Pentland Skerries are a group of small islands in the Pentland Firth, a dangerous stretch of water between mainland Scotland and the larger islands of Orkney, through which run the strongest tidal streams in Britain. The Isle of Stroma is often mistakenly included with the Orkney Islands, but is part of Caithness.