A 67-year-old man who went missing in the Hudson River during an epic marathon swim on Friday is presumed dead, according to a statement from his family.

Charles Van Der Horst, a retired medical school teacher and researcher from Chapel Hill, North Carolina, was participating in the 8 Bridges Hudson River Swim, which organizers say is the longest marathon swim in the world, when he was last seen near the George Washington Bridge at around 3 p.m. on Friday.

Van Der Horst's family issued a statement Sunday saying they were "deeply saddened to confirm the loss of our beloved Charlie."

"He was participating in several stages of the 8 Bridges Hudson River Swim when he went under at the finish of Stage 6," the statement, obtained by NBC New York, said. "He put all of his passion and zest into everything he did, from his love of his family, friends and community, to his swimming to his work on social justice and in the medical field. At this time we ask that you respect our wishes for privacy as we mourn this tragic loss."

New York Open Water, which organizes the annual event, said that at least 15 other people were swimming in the marathon at the time of Van Der Horst’s disappearance.

Participants in this year's event were to swim 120 miles at different points of the Hudson River in one week, according to the New York Open Water website. The race was divided into seven different stages, starting on the Rip Van Winkle Bridge, in upstate New York, and ending in the Verrazzano Narrows Bridge, between Staten Island and Brooklyn.

“We can confirm that all swimmer safety protocols were in place and that the NYPD was escorting the field. We will continue to work closely with the authorities,” New York Open Water said. “Our thoughts are first and foremost with the swimmer’s family.”

Authorities had stopped the search on Friday evening. They resumed it on Saturday morning with a team of scuba divers, an NYPD spokesperson said.

Stage 7 of the marathon swim, which was scheduled to place on Saturday, has been canceled.