No, you're making that up. Datacenters do not poison rivers.

To reiterate, I work in a closed loop DLC datacenter.

Pipes rust, you can't stop that. That rust seeps to the water. That's inevitable. Moreover, if moss or other stuff starts to take over your pipes, you may need to inject chemicals to your outer loop to clean them.

Inner loops already use biocides and other chemicals to keep them clean.

Look how nuclear power plants fight with organism contamination in their outer cooling loops where they circulate lake/river water.

Same thing.