Arctic char or Arctic charr is both a freshwater and saltwater fish in the Salmonidae family, native to Arctic, sub-Arctic and alpine lakes and coastal waters. No other freshwater fish is found as far north. It is the only species of fish in Lake Hazen, on Ellesmere Island in the Canadian Arctic. It is one of the rarest fish species in Britain, found only in deep, cold, glacial lakes, mostly in Scotland, and is at risk from acidification. It is also found in deep mountain lakes in Ireland. In other parts of its range, such as Scandinavia, it is much more common, and is fished extensively. In Siberia, it is known as golets and it has been introduced in lakes where it sometimes threatens less hardy endemic species, like the long-finned char.