Is that especially simpler than e.g. an attack on the above ground cabling systems by firing carbon fibre conducting wires over them, as the US is said to have done in the Iraq war? Not that I don't think underwater drones are a future risk, but the belief its a risk which can't be mitigated, or a worse risk than ones which exist onshore, seems a bit weak.

But none the less, yes. This would be a risk. Perhaps one which demands better drone detection and defence systems around wind turbines and O&G fields?