Fire department rescuers were dispatched to the area of the C&D Canal and Delaware River around 4:25 p.m. on Monday for a report of a boat in distress.
Officials said two men from New Castle were rescued and taken to Christiana Care and treated for minor exposure. A third man, who is reportedly from New Jersey, could not be located.
On Tuesday, Delaware Fish and Wildlife department sent two boats with side sonar and searchers deployed a drone to search along the shoreline.
The incident that led to the boat overturning is still under investigation.