The Lake Texoma intake vortex is a man-made phenomenon.

Open water is terrifying, even when you're hundreds of miles from the nearest shark. Sometimes, the water itself is what wants to eat you.

Lake Texoma is a reservoir located on the border of Texas and Oklahoma. It's formed by the Denison Dam and maintained by the US Army Corps of Engineers. Record rainfall in the past few weeks caused the water level to rise dangerously, so the Corps opened underwater floodgates to lower it, which formed this vortex. It's just like draining a bathtub.

Sources: US Army Corps of Engineers