Nova Kakhovka.

Russia:

1. brags about mining the Nova Kakhovka dam and threatens to destroy it if Ukrainian troops try to capture it
2. the week before the collapse issues a decree that accidents at such facilities are not to be investigated
3. when the dam collapses they simultaneously downplay the collapse and then brag about it and say they want to do it to others
4. they don't evacuate the occupied regions under flooding
5. attack flood victims in Ukrainian controlled regions

But yeah Ukraine did it.