A wave pool in China malfunctioned, sending out a massive closeout. While the wave in the video isn’t that impressive by Kelly Slater wave pool standards, it is gnarly when you consider the pool’s clientele.

The unsuspecting swimmers bobbing around in floatiess and rings were slammed into the sidewalls and barriers.

Britain’s Daily Star had a field day with the clip, describing people “running for their lives” and then elaborating, “Screams ring out across the park as the wave smashes over the barrier and knocks people over.”

Chinese media reports more than 40 tourists were taken to area hospitals with 39 being discharged shortly after. Most suffered foot injuries from failed attempts at running away.

Initial speculation is that the unknown type of wave pool had a control room failure which pumped out waves bigger than what the pool was designed to accommodate.

The system is most likely a flush, or tank system. In these types of wave pools water is drawn up into a giant tank and released suddenly to push out a wave. Typhoon Lagoon and Big Surf in Arizona work this way.

Yulongshuiyun Water Park opened to the public in 2015 and sees about half a million visitors each year. The waterpark is about a 16-hour drive from China’s specialised surfing wave pool located in Anyang, Henan, China