Whodunit
There are actually a couple good reasons for Ukraine to blow the dam as well. It wrecked the frontline defenses the Ruskies had just across the Dniper river, and actually killed quite a few of their troops. Also it will lead to fresh water shortages in Crimea. Further, it appears Ukraine was not planning an offense there as just a few days after the dam was blown Ukes are launching their long awaited counteroffensive to the northeast of the dam area. That said, the majority of towns and villages affected by flooding are on the Uke side and the tactical advantage of the dam blowing absolutely favors the Ruskies in the short run. So it's not a slam dunk as to who is behind it really, but the Ruskies are the most likely culprit.