A swimmer went missing in what was suspected to be a shark attack off a beach in California. Among the agencies searching for the missing person on Monday was the U.S. Coast Guard.

Coast Guard San Francisco Public Information Officer Grace Patton told Fox News Digital a witness had reported a shark attack to the authorities Sunday in the Wildcat Beach area of the Point Reyes National Seashore. She added that the alleged shark attack was not confirmed.

The National Park Service said Sunday that “Point Reyes National Seashore, with support from cooperating agencies, has an active search and rescue in the Wildcat Beach area” after the swimmer was “reported missing in the water.” 

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“The search continues for a missing person last seen in the water at Wildcat Beach this morning,” NPS later said Sunday afternoon. “On scene are personnel from NPS, Marin County/ Stinson Beach Fire, engines and UTVs, Reach 3 medical helicopter and a U.S. Coast Guard helicopter and Cutter.” 

According to Marin County firefighters, three men went for a swim when one of them was attacked by a shark. The three swimmers, including the missing swimmer, were reportedly camping with 15 others at an area near the beach. 

The other swimmers told first responders that they were swimming between 25 and 50 yards from the shoreline, the station added. At some point, one of them noticed a large pool of blood in the water around them, prompting that person to “scream” for the group to get back to the shore.

“Only two of the three friends returned to the beach itself,”  Sgt. Adam Schermerhorn of the Marin County sheriff’s office told Insider.

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“After searching 21 square nautical miles in ideal search conditions, we’ve been unsuccessful so far. The intent here is to continue the search,” U.S. Coast Guard Lt. Rachel Davis told CBS San Francisco on Sunday. 

The missing swimmer has not been identified. The person is believed to be around 50 years old. 

“To my knowledge, yeah, this could be the first fatal shark attack [in the Marin County area]. But we’re hopeful that he’ll be found,” Marin County Fire Department Senior Captain Ben Ghisletta told CBS San Francisco.