Watery Suckhole

For hundreds of years, people off the coast of Maine have noted a large whirlpool known as "Old Sow." It's the biggest whirlpool in the western hemisphere, and exhibits a lot of weird behaviors (including making pig noises).

Though said to be named the "Old Sow" whirlpool because it makes sounds like the grunts like a pig, it is more likely that it was actually the "olde sough" or "old drain", according to Atlas Obscura. Pronounced suff, over the years the pronunciation of the Dutch word probably shifted to "sow" (much like the word plough, pronounced pluff, turning to plow) as did the spelling and backstory of its name. (Other smaller nearby whirlpools are now known as "piglets.")

The whirlpool is caused by the enormous tides and bathymetry of the ocean floor in the area, and while it is one of the largest in the world with a diameter of around 250 feet, however the speed of its vortex does not come close to being one of the fastest. The water turbulence, while rarely a danger to larger boats, can be dangerous to man powered craft and exhibits some strange water phenomena, such as standing waves, "boils," "spouts," "troughs," "dishes," and "holes." Yes, technical terms like "holes" require quotes.

Here's a video of Old Sow in action.