Pumped hydro is really cool. Also really bad when it fails:
https://en.wikipedia.org/wiki/Taum_Sauk_Hydroelectric_Power_...
> ... catastrophic failure of a triangular section of the reservoir wall and the release of 1 billion US gallons (3,800,000 m3) of water in 12 minutes. The sudden release sent a 20-foot (6.1 m) crest of water down the East Fork of the Black River.
> A broad swath of dense forest was washed away and scoured to bedrock by the escaping flow.
A tidbit that will be interesting to any programmer or engineer: one of the causes of the failure was that the high-water gauges were moved to above the height of the dam wall because someone was annoyed by false positives.