The Ludington plant in MI is about 77% efficient iirc, not including energy for maintenance etc. It’s an open system pulling water in from Lake Mi and kills TONS of fish. Like bonkers amounts of fish, even though there are nets to try to exclude them. Also filling is mostly powered by fossil fuels today. An increasing fraction of energy to fill it comes from Renewables but that’s a work in progress. It is a steep design in a lot of ways and I am expecting new technologies will continue to be more appealing. I don’t know what the failure of the embankments would look like but I wouldn’t want to be near it myself.