Many of these offshore islands are swept by strong tides, and the Corryvreckan tide race between Scarba and Jura is one of the largest whirlpools in the world. Other strong tides are to be found in the Pentland Firth between mainland Scotland and Orkney, and the Grey Dog between Scarba and Lunga. There are also numerous clusters of islands in the Firth of Forth and the Firth of Clyde and in freshwater lochs such as Loch Lomond and Loch Maree. Outlying islands include St Kilda and Rockall the status of which is disputed.