“Radioactive water” in this context means “normal water with trace amounts of tritium, which emits radiation that is less harmful than sunlight”.

A million tons doesn't even sound like that much?

1 million metric tons = 1 million cubic meters. That's only a 100m cube of water..

It is gonna dillute so much it will not be a problem at all...

Radioactivity isn’t really a big deal for animals and non-sentients. It mostly prevents humans from entering certain areas, which in this case maybe it’s good that humans will avoid them so animals could thrive there.

What about caught radioactive fish that humans will eat?

I'd be more worried about the mercury that's already there

Once again, a problem for humans which means animals eventually could thrive

We aren't the only animals that eat fish.

The animals don’t care about radiation. They will die of something else long before they die of radiation, some might even mutate in beneficial ways.

That seems like a rather uneducated guess. Some species of shark for example live a very long time (bordering on immortal), and orcas live as long as many humans.

So you’re saying animals care.

What animals think is unknowable. It’s just as valid to say they care as to say they don’t care. We can say that they do try to stay alive as long as possible. But what does it matter what their thoughts are anyway? Physics cares about radiation, biology cares. There is no way arbitrary human-introduced tissue damage from radiation is going to be good for any creature on earth. This is wrong, no buts about it.

It’s not okay to just kill and eat fish.

You tell that to the fish.