The East Coast was hit by a tsunami earlier this month, but apparently no one was the wiser.

According to the National Oceanic and Atmospheric Administration, a rare and "complex" six-foot wave collided with the region in early June, a phenomenon currently under review, reported NPR. The wave is believed to have been caused by “the slumping at the continental shelf east of New Jersey” or a strong storm, according to the West Coast and Alaska Tsunami Warning Center.

While speculation regarding the mystery tsunami is rampant, one expert thinks the surge could possibly have been a “meteotsunami,” meaning it was not caused by seismic activity but merely a change in meteorological conditions. Paul Whitmore, an NOAA tsunami center director, said a weather system’s ability to change air pressure is enough to “generate waves that act just like tsunamis.”

A witness to the supposed tsunami, Brian Coen, told the NOAA that he saw the large wave in action while spear-fishing in New Jersey’s Barnegat Inlet on June 13. “The outgoing tide was amplified by strong currents which carried divers over the submerged breakwater. This strong outrush lasted for one to two minutes and eventually the rocks in the submerged breakwater were exposed… Brian backed his boat out before being sucked over as well,” reported the Asbury Park Press.

According to the report, the wave caused three divers to be swept off rocks, two of them requiring medical attention for non-life-threatening injuries. The tsunami, which also caused damage to boats and docks, reportedly lasted a total of five minutes.