The voice of the river awoke by Himring  

The voice of the river awoke

Warnings for canon-typical environmental damage

The Isen had not been free. Saruman had used it to drive mill wheels, poured poison into it, boiled it, evaporated it as steam… The Isen’s levels had sunk year after year, the fish in its waters had died, and so it was only too willing to be dammed up by the Ents so that it could sweep Saruman’s filth away for good. They hardly needed to ask.

As the Isen rushed down its old channel again, past the encampment of Theoden’s company and the fords were Theodred had fallen, it rejoiced, bubbling and singing to itself in the darkness.