Castle Gardens and Castle Park were evacuated and narrowboats were stopped from coming down the river. The EOD engineers then transported the devices to a nearby field where they were destroyed in a controlled explosion.
How common are these finds?
Two of the grenades appear to be examples of the ubiquitous Mills Bomb. This type of fragmentation hand-grenade was the most commonly used by the British Army during WW2. Consequently, Mills grenades are the most commonly encountered type of historic land service ammunition in the UK.
However, the third weapon appears to be a WW1-era rifle-grenade; a rarer find. The grenade used a standard rifle as a launcher. This permitted a longer effective range than was possible if the grenade was simply thrown as a hand-grenade. The device would have had a long metal rod (missing here) which was inserted in the rifle barrel. This example was also a fragmentation (as opposed to blast) weapon.
How did grenades come to be in a river?
There are a number of reasons why UXO can end up in a river. Bodies of water are ideal for disposing of hazardous items that might be a hassle to dispose of through the normal channels. Recent UXO finds and anecdotal evidence confirms that surplus ammunition was simply thrown into ponds, lakes and rivers throughout Britain during WW2. This ‘out of sight out of mind’ attitude appears to have been the norm within the armed forces.