"There's a lot of UXO in watercourses all over Europe."
There's a ton of UXO all over Europe, not just waterways. In the countryside. In the middle of cities. Peoples gardens. Hell, there was a story some years ago about a woman in Russia who was having her house repaired and the repair guy found an unexploded bomb under the floorboards. Oh yeah, she said. That came through the roof and floor. My Father just repaired everything and we forgot about it.
On the magnet fishing, this morning I was watching a video of a guy magnet fishing in Germany in a fen (it was tagged as a related video when I was watching the Tallboy in the canal go boom). He dragged up an empty 20mm shell, an empty 37mm shell, a live 7.92 rifle round, and the magazine body for a Flak 38 20mm gun, probably from the same gun that fired the empty 20mm shell he found.
The whole time I was thinking... He's going to latch onto something that's going to take his head off...
Speaking of UXO, there are still significant portions of the French countryside, especially in the Verdun area, that are off limits -- from World War I -- due to the staggering numbers of UXO underground and the huge toxicity of the soil, water, and plants from all of the heavy metals and chemicals. The French dept. of the Interior group that works to clear UXOs figures it will be centuries before those areas are recoverable... if at all.