Lake Helevorn was a deep, dark lake in Thargelion just south of Mount Rerir in the northeastern Beleriand.
According to The Atlas of Middle-earth, it appeared to span around twenty miles from its west to east shoreline.
History
After the return of the Ñoldor to Middle-earth, Caranthir, the fourth son of Fëanor, took up residence along Lake Helevorn's shorelines. During the Dagor Bragollach, the dragon Glaurung polluted and defiled its waters. The lake, along with Caranthir's domain, was destroyed at the conclusion of the War of Wrath.
Etymology
Helevorn is a Sindarin word meaning 'Black-Glass'.
Translations
References
Description
Lake Helevorn surrounded by the Blue Mountains , as depicted by Ted Nasmith