The story
The rock arch looked different on the return journey. Its opening held a slice of sky, while the water below it remained dark enough to hide almost anything. I slowed the boat and let the last wake reach the stone before making another sound.
A broad shape crossed beneath the surface. It was the sort of fish that makes a narrator immediately unreliable. I can tell you that it was large, that the water was clear and that I forgot the sentence I had been rehearsing all the way back.
I made no last cast. Instead I watched until the shape moved beyond the arch. Back at the desk, I wrote the dispatch without a measurement. The missing number is the most honest part of the entire page.
Some sightings are better left larger than the words describing them.