A shotgun was found by a dog walker on a river bank in Salford.
The weapon was discovered at around 2pm on Tuesday 31 March in a grassed area the banks of the River Irwell off Littleton Road in Kersal.
The person who found the firearm, which is partly rusted, brought it into a convenience store on Littleton Road before calling police.
Officers carried out house-to-house enquiries before arresting a man on suspicion of possession of an offensive weapon.
The shotgun is now being examined by ballistics teams and forensics experts to see if it is linked to any recent armed robberies in Salford, Bolton or Wigan.
It is not believed to be linked to the ongoing Salford gang feud which over the past two months has seen shootings, stabbings and a hand grenade thrown into a house in Duchy.
Anyone with any information is asked to call Greater Manchester Police on 101, or Crimestoppers, anonymously, on 0800 555 111.
