Amusement parks, despite their terrifying rides, are mostly safe. But accidents do happen, like the unfortunate event that took place at Shuiyun Water Park in the city of Longjing in northeast China.

Forty-four people were injured when a wave machine at the park malfunctioned, sending a massive wave crashing over the many swimmers at the “tsunami pool.” Footage from a guest shows the terrifying accident happened while the pool was packed with visitors of all ages.

“According to the initial stages of the investigation,” said the South China Morning Post, “the incident was caused by a power cut that damaged electronic equipment in the tsunami pool control room, which led to the waves in the tsunami pool becoming too big and injuring people.”

Although online rumors suggest that the wave was the result of an intoxicated park worker, it’s more likely that it was caused by a simple mechanical error. The park closed for a day for repairs, but is now open again for business.