[Retric]

We let stuff migrate upriver years ago when they added a lock system back in 1829. At this point any environmental harm from connecting these lakes has already happened generations ago well before we where born. https://en.wikipedia.org/wiki/Welland_Canal

Anyway, the amount of water flowing over Niagara Falls is currently regulated hourly by treaty with excess flows above that level used to generate hydroelectricity. 100,000 cubic feet per second (2,800 m3/s) of water flowing over the falls, and during the night and off-tourist season there must be 50,000 cubic feet per second (1,400 m3/s) of water flowing over the falls. That excess is generally 50-70% of the rivers total, 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...

[mindslight]

Connecting two bodies of water for the occasional organism that wants to pass through is a distinct thing from disconnecting two bodies of water for say large numbers of fish that would otherwise swim up a river. The latter is a usual criticism of hydro power, which seems like it doesn't apply to Niagara because it's such a big waterfall.

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.

[Retric]

I assume they sent the water over the Canadian side simply due to the treaty. That said, they have excess capacity to handle blocking 1/2 the flow over Niagara Falls every night, but even doing nothing was still a non issue.

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.