Low river flow means more of the water goes into the heat exchanger, and leads to higher temperatures. It's still ultimately due to of heating the river, it's not that there's insufficient water to actually cool the reactor, just that there's insufficient water to cool the reactor while keeping river temperatures below 28 degrees. Say there's usually 100 cubic meters per second of flow, and the heat exchanger requires 10 cubic meters per second. If flow reduces to 30 cubic meters per second that's going to raise the temperature of the river but the plant can still be cooled if the people in charge decided reducing emissions is more important than heating a stretch of river.
Whatever environmental issues caused by heating a river is tiny comparison to global warming. If say I'm handwaving environmental issues, yet you neglect to specify what I'm overlooking. If you have reasons to think that heating a river is more important than averting climate catastrophe, I'm all ears.
And lastly, plenty of nuclear power plants are cooled by ocean water, or by wastewater [1].
Whatever environmental issues caused by heating a river is tiny comparison to global warming. If say I'm handwaving environmental issues, yet you neglect to specify what I'm overlooking. If you have reasons to think that heating a river is more important than averting climate catastrophe, I'm all ears.
And lastly, plenty of nuclear power plants are cooled by ocean water, or by wastewater [1].
1. https://en.wikipedia.org/wiki/Palo_Verde_Nuclear_Generating_...