The incident happened at Davis Camp just before 8 p.m. in Bullhead City.
Reyes Augustin Munoz-Rodriguez, 35 of Fullerton, California is identified as the man who went underwater with two others, but he was the only one who didn't come up.
The three were reportedly struggling to stay above water.
"Good samaritans were able to get the two females back to shore, however, the male subject could not be located. Bullhead City Police Officers responded to search the waterways, along with Davis Camp Park Rangers, however, were unsuccessful in locating Munoz-Rodriguez," the sheriff's office said.
He's being searched for by air, land and dive crews along the Colorado River from Davis Dam to Rotary Park.
On Sunday, crews will resume searching from Rotary Park down the Colorado River to Lake Havasu.
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