The Loch Monster is an unnamed creature that appears in the Season 9 cartoon show episode "Hefty Sees A Serpent". He is a sea serpent that Hefty comes across upon his arrival in Scotland, which he tries to prove his existence to his fellow Smurfs, only to be laughed at when they don't see the creature for themselves. The creature has also been sought after by the local village fisherman Angus McGarg, who wants to prove his existence despite facing the same ridicule from the other villagers.
The creature is generally very friendly and playful, and tends to make mischief to those who try to capture him. However, when Angus finally did capture the creature by using a Smurf as bait to lure him, Hefty helped free the creature, and the creature in turn rescued the Smurfs while dashing Angus' fishing boat on the rocks, leaving him to be the laughingstock among his own people while the other Smurfs became believers of Hefty's claim.
The creature is based on the Scottish legend of the Loch Ness Monster.