It has been widely suggested that manatees (or "menatee") could be behind the myth of the mermaid. Sailors who were unfamiliar with manatees may have seen them and mistook them for the mythical, human-like species. A manatee surfacing in a patch of seaweed could have appeared to be a mermaid with long, flowing hair.
How much ocean water do you have to drink before manatees begin to look like attractive, young maidens? And if ocean madness isn't to blame here, how ugly were the women these mermaid-discovering sailors left at port if "woman" was a logical title for the first sea cow they ever saw draped in seaweed?
I should have drawn what the sailors were actually seeing, but I wanted to draw a pretty mermaid instead. Maybe another day.