I think you somewhat underestimate the difficulty of blowing this up. You have to find it first. Diving to 80 metres is _not_ child's play! Then locating the pipe with possibly poor visibility. Finally it's a big chunk of metal and concrete, you'd need the kind of explosives you can't just buy at your local corner store. I'd imagine Baltic traffic is well monitored, especially now, so if you don't want to be caught, or identified post factum, parking your fishing vessel for hours on the spot won't cut it.

That said it is well within any Baltic state's or NATO country's "easy zone".