Lyngbakr (Icelandic, lyngi "heather" + bak "back") is the name of a massive whale-like sea monster reported in the Örvar-Odds saga to have existed in the Greenland Sea.

As Örvar-Oddr and his crew were sailing southwesterly through the Greenland Sea in vengeance against the troll Ögmundr Floki, slayer of Eythjof, the deck officer Vignir knew this area would be dangerous, and made Oddr agree to sail the ship beginning the next day, to which Oddr requested Vignir advise him.

Vignir explained to Oddr that, had they landed sooner, the crew would have surely drowned.

Both the lyngbakur and hafgufa seem to have derived from a single creature called the aspidochelone in the Physiologus.

The Icelandic Physiologus contains two illustrations of the aspidochelone, one with its back overgrown with vegetation and another with gaping jaws.