Anyway, the amount of water flowing over Niagara Falls is regulated by treaty with excess flows above that level used to generate hydroelectricity. That excess is generally 50-70% of the rivers total flow with higher diversion allowed at night when fewer people will notice. Making the falls arguably just a really large and extremely expensive water feature used to attract tourism. https://en.wikipedia.org/wiki/List_of_Niagara_Falls_hydroele...
Adding a separate pumped hydro system really can be treated as an independent entity because we don’t just control the falls we can even turn it off when needed. https://www.dailymail.co.uk/news/article-1338793/Niagara-Fal...
I wasn't aware of the treaty, that makes sense.
The link about turning off the American side of the falls doesn't really support the implication that there is enough hydroelectric capacity to use up the entire flow of the river. The simplest explanation is that the flow was diverted over to the Canadian falls.
If you assume they blocked 1/2 the flow (1,400 m3/s) and didn’t use it for anything. That would still take 21 days to raise water level of Lake Erie by 1cm.
I would think the stronger argument for pumped storage would be in a place where the high level of water did not naturally exist, and so the only way it gets up there is by pumping. But perhaps this still destroys too much of an ecosystem even if it's not a river ecosystem.