An urgent search of the River Welland was carried out after a man was thought to have jumped or fallen in during the early hours of Sunday morning.
Police officers were investigating an alleged assault in the town centre at around 1.40am when a man ran from the scene and was reported to have either jumped or fallen into the river near St Mary’s Hill.
Fire crews from Stamford, Bourne and Market Deeping were called to assist with the search.
It was eventually called off when police were satisfied there was nobody in the water.
Another man was arrested on suspicion of assault and police are still investigating the incident.
Any witnesses are urged to call Lincolnshire Police on 101 quoting incident number 13 of November 20.