He's drinking from the stream, clear and cool, when something foreign brushes his muzzle--when he jerks back, he realizes it's a dead fish, the pale scales of its belly glinting in the sunlight. Suddenly, there's another one that rises to the surface, and another. More and more until the whole of the water's surface is nothing but dead and dying fish, some of them still struggling to swim in their death throes. He gags, choking up the water he'd drank, and something else is coming up as well.
With a wet thud, a dead fish drops from his mouth to the ground.