True Water-drakes, often referred to as Sea Serpents (Q. "Lingwilóki";sing."Lingwilóke), were a lesser breed of Dragon-kind believed to be remnants from the time when Ossë had briefly been corrupted by Morgoth and joined his cause, though some argued they were a corrupted mockery of Sauron's of a water-dwelling beast of the Elder Days. A plague of the seas and trouble of mariners they luckily were very rare and usually reclusive.
There were both freshwater and saltwater varieties and these hideous monsters could be found wherever the water was dark and deep. Most were deep blue or sea green in color and hard to see, particularly in the darkness. These creatures feared bright sunlight or fierce, unquenchable fires, so they rarely ventured into shallows— particularly during the day. (A host of torches could cause a Water-drake to flee.)
All Water-drakes were agile swimmers who were capable of moving at speeds of up to twenty knots (about twenty-one miles per hour). They moved almost silently and could squeeze through very small passages in reefs or cavern systems. Using its keen senses, including a sonar-like organ like that found in porpoises, it could locate its prey under the worst conditions. Then it striked with a burst of speed, as well as an uncanny sense of precision.
After successfully stalking a potential victim, the Water-drake could seize it with its six fin-claws or stun it with a blast of expelled water (treated as a waterbolt). Should either of these methods fail to make the victim tractable, the Water-drake could then try an attack with its large mouthful of multirowed, four-inch teeth. It used these to crush its prey into flexibility and then swallow it more or less whole. A larger victim could call for even more forceful methods: the long head and tail of the Water-drake made an effective whip or noose. (A larger Sea Serpent could even grapple and crush a small ship.)
Aside from the aforementioned fear of fire, the Water-drake's one weakness was its dislike of the disorienting effects of a stunning blow. Such an injury could cause the monster to flee.
Water-drakes were the most potent enemies of sailors from Lindon, Mithlond and the harbours of Gondor and perhaps one of the most dreaded beasts in the Dark Lord's employ, even though they made not much use of them, leaving them to simple tasks such as attacking unsuspecting ships and feeding of the wretched souls onboard. As possible descendants of the Dragons of the First Age the genuinity of their allegiance to Sauron was debatable, given it was not uncommon for them to sink vessels from Umbar as well.