Police evacuated homes in the Stamp End area of Lincoln on Sunday night to carry out a controlled explosion of a suspected grenade.
Magnet fishermen pulled out what police believe to be a grenade from the river at around 4pm before police cordoned off the area for several hours.
At around 11.30pm, police evacuated homes in the Stamp End area of the city and a team from the bomb disposal unit carried out a controlled explosion.
People were allowed back into their homes just over half an hour later at around midnight.
Detective superintendent Mark Kirwan said: “On behalf of all of the emergency services I would like to thank all the residents for their patience and support in bringing this incident to a safe conclusion.”