Police and the Explosive Ordinance Disposal (EOD) team from the army were called to Gibraltar Point Nature Reserve on Friday evening.
After x-raying the device, the EOD said it was an old practice bomb but was not live. A spokesperson for Lincolnshire Police, said: "We were called to Gibraltar Point at around 6.30pm after an object was discovered by a dog walker.
"EOD attended and x-rayed the device, which turned out to be an old practice bomb.
"It was not live. The team made it safe and took it away."
Gibraltar Point has thanked the emergency services for dealing with the incident. A post on social media said: "Many thanks to Lincolnshire Police and the Bomb Disposal Team for dealing with a slight issue on the beach Friday night!"
However, it got some readers wondering what other wartime relics are still out there - although one person thought the picture was a seal.
Mary Porter said: "Oops! It is scary how much of that stuff is still about. I dug up a grenade in my garden in Felixstowe, Suffolk, years ago.
"I called the police who came round. We all looked at it (I had wiped it clean of mud so they could see it clearly!) and they declared, 'It's a grenade' and I replied,. 'Yes, I know, that's why I called you'. Two days later, the bomb disposal came around, popped it in a bucket of sand, and drove away with it!"
Fiona Sheep said: "Looking forward to a interesting talk and dinner after an afternoon walk."
Helen Freeston said: "At fist glance I thought it was a sea. They have ginger ones down in Essex!"