Comment by pm215

The OED agrees about the Dutch idea, giving the etymology as:

"early modern Dutch maelstrom (now maalstroom) whirlpool < malen to grind, to whirl round (compare meal n.1) + stroom stream n"

and also thinks Dutch is the origin, with Swedish/Danish etc taking it from Dutch too:

"The use of maelstrom as a proper name (also in French) seems to come from Dutch maps, e.g. that in Mercator's Atlas (1595). There is little doubt that the word is native to Dutch (compare synonymous German regional (Low German) Maling). It is true that it is found in all the modern Scandinavian languages as a common noun, but in them it is purely literary, and likely to have been adopted from Dutch."