It’s 76 metres in diameter, has sucked a dozen sailors to Davy Jones’ locker yet is a vital lifeline for marine animals – this is the world’s second largest tidal whirlpool.
For a couple of hours about twice a day, the waters of Passamaquoddy Bay churn and bubble, creating an enormous swirling eddy.
Measuring around 76 metres (250 feet) in diameter, this is the Old Sow: the largest tidal whirlpool in the western hemisphere and the second largest in the world. It’s dwarfed only by the Maelstrom of Saltstraumen in Norway.
These gushing waters – located between Deer Island, New Brunswick in Canada and Moose Island in Maine, USA – are most visible a few hours before high tide.
The gigantic whirlpool is created by the movement of water around the around the unusually shaped bay, which is full of underwater mountains, trenches and narrow passages.
As the tide comes in, “a tremendous amount of ocean water, called a current, flows swiftly into a confined area called the Western Passage before emptying upriver into Passamaquoddy Bay,” explains NOAA’s National Ocean Service on its website.
“After making a sharp right turn to the north and traversing a deep trench, flowing past an underwater mountain, and encountering several counter currents, a portion of the current "pinches off" to form the huge circular current called Old Sow,” NOAA writes.
This main whirlpool is also surrounded by lots of smaller vortexes, affectionately known as the Old Sow’s piglets.
The rush of water flooding into the whirlpool makes a huge racket. “According to folklore, the name refers to the "grunting" noise — which sounds like hungry pigs slurping up their slop — made by the giant churning gyre,” says NOAA. "Sow" may also be a mispronunciation of the word "sough" (pronounced suff), which means "sucking noise" or "drain."
Historically, this whirling vortex destroyed several boats, drowning the unlucky sailors onboard. Around a dozen people are said to have died here.
Today, experienced skippers with motorboats can safely navigate the whirling waters and tourists who visit can buy a certificate to prove they survived the experience.
Despite the potential danger to small boats, the Old Sow a lifeline for marine life. “Even though it’s really powerful, whales, porpoises, seals, thousands of birds will come in here to feed,” says birdwatcher Bob Duchesne in a YouTube video on birding at the Old Sow.
The churning waters bring cold, nutrient-rich waters up from the deep to the surface, providing a feast for ocean animals.
“The whole channel is like a rushing river,” says Duchesne. “It takes small critters from the bottom where they’re safe and pushes them towards the surface where the big critters can eat them.”
This makes it a great wildlife watching spot. Whale watching boats regularly visit these waters looking out for minke whales, porpoises and seals.
Duchesne loves to visit to see all the different types of birds. “It may be the most popular birding spot that nobody knows about,” he says, adding that he often sees puffins, razorbills, common murre and more. “They know where the food is.”
