This is a rip current, a strong flow of water that moves off shore. It's dangerous, probably the deadliest thing that can be encountered in the ocean. More than one hundred people drown every year because of it.
I had the feet in it initially, not in danger but annoyed by the strong pull, I moved aside. Reading later the story of Playa del Amore y del Divorcio (this one), I realized what it was. - 2 months ago