Might not even need divers. Just a fishing boat, a GPS, a limpet mine, and a few hundred feet of rope. Dangle the mine in the water at the right depth as you cross the path of the pipeline and let go when it attaches. Set the timer for weeks or months so you're long gone by the time anyone starts investigating.
(If the pipelines are made of a non-magnetic material like stainless steel maybe you'd need to do something more sophisticated.)
Maybe we'll know more once investigators inspect the damage, but I think practically anyone could have done this based on what we know so far.
Sections are shallow. (No clue about the blast sites.) With zero information on the extent of the damage beyond measured pressure drops, folks dropping weighted dry bags of dynamite from kayaks is in scope.
Germany has an option to talk with russia to make a deal, so russia reopens the valve... some other forces don't want that.
It is a 101 of economical warfare.
With the closed valve, they have an upper hand at negotiations about gas, especially if the german people get cold and start sharpening the pitchforks for their own (german) politicians... now, even if the germans want to negotiate, there will be no gas until the pipelines are fixed, and it doesn't seem that will happen soon
Nobody believes in their 'repairs' and temporary issues with the pipeline. I really hope it is destroyed.
If they wanted they could reuse the old pipeline that is on land on Polish territory.
BTW. It is not only my suspicion: https://www.politico.com/news/2022/09/28/nord-stream-pipelin...
Ukraine isn't on the Baltic Sea, but do they need to be? Honestly, I don't know the resources that would be required to accomplish this. Would some special forces with diving equipment and a fishing boat be enough?