What was that?

I was walking down to the Canoe Club when I saw a couple frantically paddling a double-kayak to the dock. The kayak was tilted towards the back and seemed nearly flooded, but they managed to bring it safely into port. When the inundated boat was hauled out of the river I saw the source of the trouble: the tip of the boat was gone. The yellow plastic ended in a strangely smooth way, as if it had been left in a strong acid. The couple stood on the dock looking dazed and lost. I approached them and asked what happened. They both looked up at me in surprise, as if jolted out of a daydream. Then, slowly, with both trying to talk at the same time, they told me:
They had been kayaking down the river, just having a day in the sun. Paddling along, more absorbed in eachother than their surroundings, they paid little attention to where they went. Slowly and unnoticed, a mist crept across the water, arriving silently on slippered feet tiptoeing over the water, it surrounded them. Suddenly they noticed the change: surrounded by a whiteout, they could only see a scarce few feet from the boat. They laughed nervously at the novelty of it, but the mist swallowed up the sound, making them silent with unease. The water had calmed, smooth as glass but just as impenatrably murky as before. The river seemed to absorb their cautious strokes: what ripples were created disappeared quickly as the water remained resolutely calm. Thinking logically, they made their way for shore, but land never came. Pushed by an unspoken fear, they paddled faster, but no matter how they flew over the glassy surface all they found was fog. Then, a disturbance, ripples in the water, this time spreading quickly across the surface. Again, from the left, the power of the displacement rocked their boat--but soon all was still again. Defensive now, they frantically scanned the vague waterscape, looking for the threat. Suddenly, out of the water loomed what could only be described as a massive catfish. It opened its gaping maw and latched onto the back of the kayak. A horrible sucking noise broke the silence and the beast began swallowing their boat. Screaming, they both took up arms and hurredly slapped at the fish with they paddles. Seemingly surprised by the ferocity of their retaliation, the monster fish sunk back beneath the waters, claiming the back end of the kayak. Their fight done, flight took over, as the couple paddled furiously away from the behemoth. To their relief, spears of sunlight streamed through the mist, chasing it off. Apparently they had gotten completely turned around, since the Canoe Club was now in sight, towards which they paddled before they were swamped.
They finished their tale slowly with great difficulty, as if they couldn’t quite remember the details. I would have asked them their names, but I never got the chance. After telling their account, they broke off, their eyes unfocused. Staring blankly, they walked aimlessly away until one of the employees interrupted, asking just what had happened to the kayak, to which they monotonasly stated that they must have hit a rock.