The Bloodmaw actual diameter has never been recorded. Estimates range from a yard to a mile. But most agree that the thing is only about 50 yards in diameter. It is a perpetual maelstrom. There are two odd things about it, however. The first is that the ocean, for about a half a mile around it is crimson. This crimson color is caused by red dirt, found on the bottom of the ocean, which is forced up by the maelstrom. The other is that the Bloodmaw is covered by a storm. This storm varies markedly. On some, its only a stiff breeze. On others, all stops are pulled out. Pelting rain, hail, lightning, wind, dirt clods (picked up by the wind from the ocean). The air, on these particularly violent days, is usually crimson from flying specks of dirt, reminiscent of a sandstorm in the desert. This storm can go from one extreme to the other and back again in an hour, but will usually stay at one level of intensity for around a day. Storms are always violent around the equinoxes and solstices, with almost constant deadly storming for the weeks before and after the day. No one much else about the Bloodmaw, because no one is willing to go near it.
Note: Most of these legends and tales have a grain of truth to them. There were two sea gods in the area, and one of the religions worshiping him has disappeared. There were three wizard wars. Giant Sharks have plagued the seas nearby. That being said, all are wrong. The Bloodmaw's purpose is the add decoration, strategic depth, etc. to a map, not to provide a quest, though
Sea God: One tale about the Bloodmaw says that there was once two sea gods who ruled over the seas. But once the peoples worshipping them came in contact and began to merge, competition between the gods grew more and more fierce, until it disintegrated into true holy war. The seas boiled as the two gods fought, and they churned and frothed, wrecking death on all near the shore. The religions armies fought on land, seeking to destroy all who worshiped the foe's god. And at last, after five years of fighting, the old god died. His essence melted into the area, changing it forever. The water turned red, the maelstrom churned, and the storm killed. Most sailors (even if they don't believe this tale), when they need to pass by Bloodmaw, throw a sacrifice into the red water, to be sucked in, to placate the dead god. Whether or not this works is unknown- if it fails then there isn't going to be anyone to tell tales.
Magic War: The more history-minded sailors think that the the Bloodmaw was formed of a spell that went wrong in WWI (Wizard War One). Instead of turning each brick of the Abez tower into a Shnickel (I have no idea how to link these to other subs in the Citadel, so I'll just say search it), it hit the Abez tower's spell, and blew up. This formed the Bloodmaw. Even now, the Bloodmaw turns and kills by using raw magic as a power source.
Sharks: The local sea god has some pets. Two giant sharks. Most subscribers to this particular tale say that they are 30 yards long, and 10 yards high, but some go higher, others lower. The sea god uses these sharks as his servants- when he needs something, he sends them. The sharks, when they have free time, chase each other in an eternal circle. This spins the waters, creating the Bloodmaw. When the sharks are serving the sea god, the Bloodmaw slows down, and becomes less deadly. When the sharks chase each other, it becomes more deadly. The bloody sea comes from fallen victims.