According to a Universal Studios Hollywood spokesperson, it happened during an afternoon performance.
Initial reports indicated there was a possible drowning.
The Los Angeles County Fire Department said a man required CPR when they arrived.
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"Our thoughts are with him as he receives care," said the amusement park spokesperson. "Details surrounding the event are being reviewed."
A witness who spoke with our sister station KABC said it all unfolded during a WaterWorld performance. He said the performer was on one of the towers, and, as part of the act, fell into the water.
The witness said the other workers noticed he was missing and went in the water to pull him up.
In video obtained by KABC, several people are seen pulling the performer to an area behind the scenes.
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The witness said the show was suddenly canceled and guests were escorted out.
The condition of the performer remains unknown.