Do not just look for the animal - read the sand.
Stingrays can be surprisingly easy to swim past. Their colors, patterns, and quiet movements help them disappear into the seafloor.
A diver who is moving too fast may see only sand, ripples, scattered seagrass, and coral rubble. Slow down and look again. A raised edge, a pair of eyes, a tail line, or a small puff of sediment may reveal the animal that was there all along.