The Fellowship of the Ring
"Hey there, Aragorn!" shouted Boromir, as his boat bumped into the leader. "This is madness! We cannot dare the Rapids by night! But no boat can live in Sarn Gebir, be it night or day."
"Back, back!" cried Aragorn. "Turn! Turn, if you can!" He drove his paddle into the water, trying to hold the boat and turn it round.
"I am out of my reckoning," he said to Frodo. "I did not know that we had come so far: Anduin flows faster than I thought. Sarn Gebir must be close at hand already." (2.9.42-4)