Creative Speculation

http://www.inquisitr.com/258095/baltic-sea-ufo-really-just-rocks/

snip:

The Baltic Sea UFO is more likely a rock formation that occurred where fluid or gas vented, Charles Paull of California’s Monterey Bay Aquarium said in an interview with Popular Mechanics.

Hanumant Singh, a researcher with Woods Hole Oceanographic Institute, also told Popular Mechanics that the images of the alleged Baltic Sea UFO released by the team had several inconsistencies. For one, they were taken with an inexpensive type of sonar that contained several distortions. The picture also revealed a reflection of the image that indicated the instruments weren’t properly wired, Singh said.

Ocean X is something closer to a treasure hunting team than aquatic observers. The team is mainly focused on finding sunken treasures, including champagne bottles from a shipwrecked Swedish schooner, The Los Angeles Times reported. The report questions whether the Baltic Sea UFO was maybe nothing more than an attempt to market the undersea adventurers.

The picture in the OP is an artist's rendition. When I looked at photos of the object, my first thought was that it could be a concretion.