After Russia blew up its own pipeline they had experienced divers who could blow up the dam they control whose resevoir feeds cooling water to the nuclear power station Russia controls and also feeds fresh water through a canal to Russia's most important naval base on Crimea, where the lack of fresh water after Ukraine blocked the canal was one of the principal reasons Russia gave to start their invasion in the first place. The flood waters affect Russian troops far more than Ukrainian troops.

Or Ukraine blew up the dam after discussing openly in December about blowing up the dam and even practicing shooting the dam sluice gates with HIMARS rockets. After the dam was breached, Ukraine has continued to release a higher than normal amount of water upstream which has increased the flooding and devastation to downstream civilians.

Which scenario is more plausible?