Europe: coastal waters and rivers of north-western Mediterranean Sea , along European Atlantic coast, North Sea and the whole of Baltic Sea. Absent from Black, Caspian and Polar seas. Landlocked populations from Lake Mjosa in Norway , Lakes Ladoga and Onega, upper Volga in Russia, Loch Lomond in Scotland, some Finnish lakes and possibly in Lough Neagh in Ireland. Appendix III of the Bern Convention. Protected by law in the Netherlands.