I thought that if it came to an emergency they could keep the reactors running, only the exhaust water would be too hot and river wildlife would die around the vents.

France has already upped the maximum temperature legally allowed two or so years ago. And while short term that is a solution, the fact is that us humans need working ecosystems to survive. It's not just fishers being impacted, ecosystems are connected and we're cutting into them at record pace anyway.