Sea zombies (also known as drowned ones) are the animated corpses of humans who died at sea. Although similar to land-dwelling zombies, they are free-willed and are rumored to be animated by the will of the god Nerull the Reaper (or another similar evil deity).
The appearance of drowned ones matches their name: they look like human corpses that have been underwater for some time; bloated and discolored flesh dripping with foul water, empty eye-sockets, tongue frequently protruding from between blackened lips.
Their visage and the stench of decay surrounding them are so disgusting as to cause nausea in those with a weak stomach. Those who come into contact with the drowned ones are prone to severe disease. On land, drowned ones move slowly, with a clumsy, shambling gait. In water, however, they can swim with frightening speed.
Drowned ones have an abiding hatred for the living and attack them at any opportunity. These attacks often show surprising cunning (for example, luring ships onto the rocks and attacking the sailors as they try to save themselves from the wreck). Drowned ones take advantage of their swimming speed by attacking ships as they lie at anchor -- climbing aboard the vessel and trying to drive the sailors overboard, where they can deal with them more easily.
Drowned ones attack with the weapons typical of sailors: short swords, daggers, hooks, clubs, belaying pins, etc. Some are even capable of spellcasting, as they were priests while alive, and they retain their powers as undead. They normally stray no more than 100 yards from the water, but sometimes will roam inland if the wind and the fog create the right conditions.
Note: Zombies originally appeared in this form in the 2nd Edition Monstrous Manual for the AD&D game from TSR. Their use here is for the purposes of providing context for the campaign only.