Lincolnshire Fire and Rescue crews were called to reports of ‘someone in the water’ in the Fishtoft area last night (Thursday).
A spokesman for the service said it was called to the incident by police at about 10.47pm.
Two crews attended from the Boston Water Rescue and whole time team and the Boston retained crews.
Thermal imaging cameras and lighting were used to search the river and banks, however, nobody was found.
Residents in the area also reported a National Police Air Service helicopter in the area.
A Lincolnshire Police spokesman said: “We were concerned for the safety of a man who was believed may have gone into the river. NPAS were assisting us. The search did not uncover any persons.”
The National Police Air Service has also been contacted.