1 - A river at the base of a waterfall. There is lots of debris floating about - a broken canoe, paddles, general supplies (bags, food, etc), and so forth.
2 - A shadow is visible in the water, coming up to the surface. Maybe some air bubbles as well. You know, the usual.
3 - Tonto swims up and pierces the surface of the water, taking a huge gulp of air.
4 - Tonto treads water, looking around him. It's mostly the same debris floating along with the current.
5 - Pull back a fair distance. Tonto continues to tread and search; everything else continues to be pulled by the current. The Lone Ranger is nowhere to be seen.
LETTERING NOTE: The word balloon should be big to emphasize that Tonto's really belting out his call.