Del Prete was tubing on the river with a group of about 10 other people when he fell off his tube while trying to paddle to shore last Saturday, Aug. 10.
Del Prete's mother told the news website NJ.com that he had recently moved to Herndon and was working for the Department of the Interior. She said he was a strong swimmer.
Authorities told NJ.com they now have reason to believe his body may be trapped underneath a whirlpool.
Del Prete's family also told the news website they want to work with local officials on a flag-warning system on the river to help warn tubers, fishers and swimmers of the dangers when river levels get dangerously high.
According to NJ.com, four people have died this year on the river, and a search is also currently taking place for a New Jersey man that went missing in a similar incident.
READ: Herndon Man Believed to Have Drowned on Delaware River
FOLLOW HERNDON PATCH FOR THE LATEST NEWS AND EVENTS!Facebook | Twitter | Daily & Breaking News E-mail Updates