Two amateur magnet fishers - a hobby in which people use magnets tied to ropes to "fish" for metal in water - say they were shocked when they pulled a World War Two grenade from a canal.
Tony Randall and Ian Nicholson discovered the weapon on Tuesday.
Police set up a cordon and closed Wistow Road, near Kibworth. A controlled explosion was carried out.
The pair also attracted police to the canal last week when they found a safe they thought may have been stolen.
The friends said they only took up the hobby two weeks ago.
Mr Randall, from Countesthorpe, said: "That's twice in as many weeks we've had to call the police out.
"It was Ian who actually pulled the grenade out and said, 'Hey, look at this! It's a hand grenade' when I was just a few feet away."
Mr Randall, from Leicester, said: "When you see the bubbles coming up, you know you've got something and you gently pull it up - very gently in this case."
An Army spokeswoman said: "Destroying the grenade was the safest thing to do as old ammunition can be quite unstable."
She urged anyone who finds any suspect items to not touch them and to alert the police.