The following is a story recounted by Jacques Yves Cousteau in his book The Living Sea:

Some miles ahead, there was a barrier of foam across the horizon. "There can't be a reef here in the ship lane," I said...The reef seemed to sway. A half-mile from it we saw the splashing breakers were composed of leaping dolphins, the most formidable host that I had seen in a quarter of a century at sea.

The Captain rang the bridgehouse bell to rouse evryone out to see them. The dolphin army wheeled and charged toward us in a storm comber that erupted twisting black bodies into the air. A nation of dolphins had gone mad before our eyes.

Dolphins, of course, are air-breathing mammals, and we were familiar with their light, measured prancing into the air to breathe. But these were shooting vertically high out of the water, bending and contorting in the leap. It was a mass high-jump contest, a bridal feast, or a frenzied victory celebration after some unknown war in the deep...

For the rest of the day Calypso was steered by dolphins, obeying the whims of the flying phalanx spreading before us to either rim of the ocean. I took a rough sighting on their jumps. Their tails were clearing 12 to 15 feet. As they fell, they twisted into awkward postures, as if vying to smack the water in the most ungraceful way. I tried to estimate how many there were. At a given minute, there were about 1000 out of the water on jumps that averaged 3 seconds. For one in the air, there must have been 19 in the water. Perhaps 20,000 dolphins formed the living reef.