Lurkers

Lurkers are vermin that infest the sewers of Britannia and the rivers and lakes of the Underworld. The traveler who must venture into water will be particularly vulnerable to the Lurker's particularly potent bite and strong grasp of tentacles.

It has been surmised that Lurkers do not possess the underwater breathing capabilities of fish; thus, they must surface to breathe. Indeed, many travelers have noted that Lurkers may linger on the surface of the water, waiting for scraps of garbage or easy prey. It is fair to assume that Lurkers are more of a scavenger than predator, but it would be wise to avoid these creatures all together. Employ missile weapons, from a safe distance, when possible. If you encounter a Lurker in open water, be prepared to defend yourself as they are quite agile.

Note that these Lurkers have nothing in common with the Lurkers of Pagan.

Lore
''For the most part, these tentacled monstrosities have been more of a nuisance than a threat. Lurkers dwell in the subterranean rivers and channels of the Abyss, and have never been seen on land. They are normally seen floating just below the surface of the water, with their eyes and yellow tentacles poking out above. We know of a few cases in which a Lurker has pursued a swimmer, and once a beast became so enraged that it lurked at the water's edge and attacked those along the shore. Knight Willomar tells of encountering a more ferocious variety of Lurker in the deeper catacombs. This Deep Lurker is reportedly a veritable giant. (We do not know if it is a lone monster, or one of a new sub-species.) Its great size could not be detected from the small profile it presented above the water, but the Deep Lurker should be recognizable by its distinctive green color. Willomar spent many days recovering from his battle, and was for a time wracked by a mysterious fever that poisoned his brain, but we do not know if the disease came from the monster or from some other source.''

- from "The Memoirs of Cabirus", Ultima Underworld

''Lurkers are usually seen floating just beneath the surface of a secluded lake or subterranean pool. They rest with their eyes and a few tentacles poking just above the surface, alert for predators or prey. In most cases, lurkers will not bother anyone who  does not actually  enter  the  water, although they may track a person's position, and follow along behind him. They present a greater danger in the water, however, as they are well-adapted to water-borne combat, and their body-mass alone is enough to bar a swimmer's way in a narrow strait. As lurkers sink out of sight when killed, it is unclear whether they breath air or water, or what shape their lower body takes.''

- from "A Safe Passage through Britannia", Ultima Underworld II