Officials say at some point, fellow competitors in the "8 Bridges Hudson River Swim" noticed 67-year-old Dr. Charles Van Der Horst was gone.
Police have not officially released the identity of the swimmer, but The University of North Carolina School of Medicine released a statement identifying the swimmer as Van Der Horst, a retired professor who worked in the Division of Infectious Diseases.
Stay on top of breaking news stories with the ABC11 News App
"The UNC School of Medicine is shocked and saddened at the news Dr. Charles Van Der Horst has been reported as missing following a multi-day swimming race in New York's Hudson River. Our thoughts are with Dr. Van Der Horst's family at this time," a statement from the UNC School of Medicine said Saturday.
According to our newsgathering partners at the News & Observer, Van Der Horst was an internationally known AIDS researcher.
"Dr. Charlie Van Der Horst's life and and work were defined by compassion. From his time volunteering in North Carolina's free clinics to his efforts on the front lines of the HIV/AIDS epidemic, he made our state and our world better," Gov. Roy Cooper said in a Tweet on Monday. Cooper earned his undergraduate and Law degrees from UNC.
The New York City Police Department called off search and recovery efforts. Monday morning.
The swim has seven stages. Friday was stage six -- 15.7 miles from the Tappan Zee Bridge to the George Washington Bridge.
New York Open Water, a non-profit handling the marathon swim released a statement Friday night saying in part:
"On behalf of New York Open Water, it is with great sadness that we report the loss of a swimmer today on Stage 6 of the 8 Bridges Open Water Swim. Our thoughts are first and foremost with the swimmer's family and in respect for their privacy, we are declining to name the swimmer at this time."