In The Fellowship of the Ring, the heroes encountered a tentacled beast in a swampy, stagnant lake. After trying to make their way across Caradhras during a deadly blizzard, the Fellowship was stopped in their tracks by Saruman, who was putting a curse on the Mountains of Moria to try and bring it down and stop the Fellowship from going any further. The Fellowship was buried in snow on the dangerous path when Boromir said they needed to get off the mountain for it would be the death of the hobbits. Gimli had mentioned the group could pass through the Mines of Moria, but Gandalf was weary of traversing this path due to the Balrog.

Nevertheless, Gandalf let the Ring-bearer—Frodo—decide which path they would take. And of course, Frodo chose to go through the mines since Gandalf didn't let on why they shouldn't. When the Fellowship reached the Doors of Durin (or the West Gate of Moria), it reflected the moonlight, showing two ancient trees with an Elvin riddle. The riddle stated "speak friend, and enter." Gandalf spent quite a long time trying to open the doors, for he had never gone into the mines this way. In the movie, it was Frodo who solved the riddle, which was actually quite simple, as the password was merely the Elvish word for "friend"—which was "mellon."

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But while Gandalf was busy trying to open the Doors of Durin, Merry and Pippin (of course) were up to no good—carelessly throwing rocks into the black lake. The ominous music and camera angle suggested something evil was lurking nearby. Aragorn grabbed Merry and Pippin, and he warned them to not disturb the water. But it was too late. At the last second, Frodo was able to figure out the riddle, and the Fellowship made their way inside the mines with Aragorn slowly backing away from the water—alert for what may happen next. But when Gandalf used his magic to illuminate the dark mines, Boromir realized this was no mine, but a tomb, and every one of the dwarves had been killed.

This is when the tentacled monster attacked, grabbing Frodo by his ankle and dragging him out into the black lake. Sam was able to initially get Frodo away from the beast, but it took the whole Fellowship to be able to free him. In the film, Peter Jackson's version of the monster resembled the Kraken, but Tolkien never described it this way and only stated that the monster had twenty-one tentacles. In the book, this monster was called the Watcher in the Water. Not much is known about this creature, but it is said the Watcher was responsible for creating a dam that blocked Sirannon River.

This blockade caused the lake water to become deeper, which resulted in the narrowing of the pathway in front of the Doors of Durin since the water's edge had crept so close over a long period of time. Gandalf was initially scared to enter the Mines of Moria due to his fear of the Balrog, and Saruman also knew of Gandalf's reasoning for his hesitation. Gandalf said something had "crept or been driven out of the dark water under the mountains. There are older and fouler things than Orcs in the deep places of the world." In the movie, Gandalf only says the line about older and fouler things, and because of the context, the audiences assumed he is only talking about the Balrog seen in Saruman's book.

But it's possible Gandalf had anticipated there being other large and dangerous monsters in and near Moria because the Dwarves had dug too deep and greedily. Óin, Gimli's uncle, described in the Book of Mazarbul that the Orcs had taken the Bridge of Khazad-dûm, and the Dwarves only way out was through the Doors of Durin. But because the tentacled beast had built the dam, the water was right up to the edge of the door. It is implied the Watcher in the Water tore apart and ate Óin. It is not known what type of creature or species the Watcher is, only that it is malicious. The creature, like Smaug, seems to also act independently of Sauron.

Many Tolkien fans have theorized that the Watcher in the Water lived in the deep waters under the mountains until it was freed and made its way to the dark lake, where it watched and waited for any creatures to pass by so it could feed on them. Although the monster seems to target Frodo (who is carrying the Ring) and tries to eat him, many still think the creature is far too old and powerful to be caught up in the troubles of the world. This Lord of the Rings monster is much like a Lovecraftian being who's likely been around for many centuries.

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