Maelstrom was a spell used by powerful wizards in Zakhara, the Land of Fate.
When cast upon a large body of water, this spell created a hole through the Prime Material Plane into the Elemental Plane of Water, creating a huge whirlpool for the duration of the spell.
The mouth of the whirlpool was 300' (91.4 m) wide and sucked down ships unless they were controlled by the best sailors.
Living creatures sucked through the portal either drowned on the Elemental Plane of Water or were enslaved by marids.
This spell required a diamond worth at least 1,000 gold pieces to cast.