What are those dark spots in the ocean? Here’s why lifeguards want you to avoid them

Dark blue spots have been seen off the Myrtle Beach area coast on Sunday and have caused some confusion.

A Facebook Post on Sunday with more than 1,500 shares and 4,000 comments claimed that one of the bait balls was a submarine spotted off the coast.

But the black spots aren’t submarines–they’re schools of fish known as bait balls that lifeguards see every year.

As Myrtle Beach area waters warm up for the summer, many more fish, including predators, are swimming through the Myrtle Beach area as they migrate north to cooler waters.

People may see schools of fish closer to the surface, creating what looks like an oil spill or black ball in the ocean as small fish look for food and crowd each other as a survival technique, Nick Jackson, co-owner of Myrtle Beach Surf Rescue, said.

But these massive schools are a safety concern.

“They school up to kind of trick predators–I guess you’d call it a defense mechanism–instead of a single fish swimming around,” Jackson said. “It’s very common to have different species of fish school together and come to the surface, especially close to shore, this time of year.”

Predatory fish such as sharks or barracuda may come to the surface to grab a snack from some of the hundreds of fish in a single bait ball, Jackson said.

Because of the increased chance of a shark or other predator mistaking a human swimmer for a snack, lifeguards pull people inland from the water when they see one of the black spots show up.

“Statistically speaking, you have a higher chance of getting struck by lightning than you do getting bit by sharks, but we have had shark bites in the past,” Jackson said. “It’s always from a case of mistaken identity.”

Bait balls haven’t recently caused someone to suffer from an attack or an unlucky encounter with a predator, Jackson explained.

“We have had other rescues as far as a water standpoint, just from rip currents and whatnot,” Jackson said. “But not from schools of fish.”

This story was originally published June 23, 2025 at 2:17 PM.