Eek... Is there really no responsible way to deal with this? It must be possible to clean the water somehow. I assume it's contaminated with radioactive particles which could just be filtered out. Expensive I'm sure but they should clean up their own mess, not dump it in the environment.

If it's just heavy water (like water molecules with deuterium/tritium), those are actually a commodity. So I don't assume this is the case.

Also, any technology developed for this purpose will help cleaning up future nuclear disasters. There's several naval nuclear reactors and some weapons rotting away on the ocean floor and even some in orbit waiting to fall down eventually.