Their point is not to actively trigger an emergency at a given time. If a bomb is undisturbed at the bottom of a water body it is not bothering anyone and actually is providing artificial reefs for marine life. Should it be found one day and removed? Yes probably. But should it be brought to the surface by amateurs and need immediate reaction? No.

>Should it be found one day and removed? Yes probably

Let's not pretend that any government is going to take it upon themselves to sweep their country's waterways for unexploded ordinance. Come on.

The hope is that it lays undisturbed long enough to be rendered inert.

Bomb detonators aren't rendered inert just by sitting there. Delay fuses consist of a thin sheet of plastic that retains a lever and is dissolved by a quantity of acetone in an ampoule that was opened upon release of the bomb. About 20 % of the ordnance dropped over Germany by the Allied Forces was equipped with delay fuses, designed to disrupt fire and emergency services after a bombing raid. There is about one explosion/year in Germany, 72 years after the end of the war, and no end in sight. Yes, the German authorities are still actively looking for unexploded ordinance and are using Allied target photography because you don't want to hit a live bomb during excavations for a new building. Remember, the detonator is mechanical and easily triggered by vibration and movement. No, you don't want 250 kg of high explosive going off, even if covered by 1.5 m of water. In the UK they are doing similar.

> unexploded ordinance

It's "ordnance", not "ordinance".

organ stance?

a bomb at the bottom of the water in Britain (given the historic context of Germany bombing) has probably detonator in the armed state. The detonator just didn't triggered back then because for example the bomb hit the mud (naturally for the bomb falling into the river). That detonator still has high chances of going off in any moment as result of rust and/or any disturbance like from a boat passing too close. So the earlier such bomb is found [by anybody] and is removed by professionals the better. (back then, during the 4-6th grades, we found and "responsibly" disposed off [in a campfire in a forest outside the city] a range of WWII munitions. All without detonators of course. The detonator makes huge difference and we wouldn't touch the stuff with it attached - didn't even attempt to check the state of the detonator, after all we were after the fun, not suicide)

Depending on the depth; it's probably safer going off in the water. 5' of water is going to dampen most explosions better than a boat hull.

And if it's armed, as you indicate, it's an even worse idea to use magnets around it.

Sounds like they're kind of like asbestos. If you don't mess with them the harm is essentially nil.

It's when you start dragging them out of the water with a magnet that the risk ramps up.

Until the asbestos is disturbed by some accident and now everyone around has been exposed to it, like dropping a heavy object on a floor tile.

> a negative light on ordnance being voluntarily removed from waterways?

Voluntarily being removed by amateurs without safety equipment.

And in deep enough water, an explosive is effectively neutralized anyway.