A lifeboat and rescue helicopter were scrambled after reports of a person in the sea off Skegness beach.
An air ambulance was also called and landed on the beach, close to the lifeboat station, at about 17:45 BST.
A spokesperson for the RNLI said the inshore lifeboat was launched and CPR was carried out on a person.
Humber Coastguard, which covers the area, confirmed there was an incident and said it had “everything on it”.
