Some sea lion pups paddled tentatively in the shallow surf, learning to swim at Punta Norte beach in eastern Patagonia, and we were staring at the sea, watching for a huge black fin.
It was my first visit to see orcas hunting baby sea lions on the Valdes peninsula, a natural phenomenon unique to the killer whale group in this region.
I tried to stick carefully to the instructions the park ranger gave us before leading us to a thin stretch of sand near the ocean where Mel, a giant orca, was preparing to hunt.
Six of us - a Reuters cameraman, the park ranger, three nature photographers, and I - were waiting to see one of the animal world's most spectacular attacks on this beach, where killer whales swim up a channel of deep water to get right onto the sand. They risk death if they become stranded.
Stretched out like sharp-shooters 30 yards from the water's edge, we watched, transfixed, as an enormous black fin approached one wobbly pup in the shallow water.
An instant later, Mel torpedoed toward the beach at full speed, hidden in a wave and throwing his nine-yard-long body completely out of the water to grab the pup in his jaws.
It was almost soundless. All you could hear was the break of the waves as the orca shook the sea lion and wiggled his enormous body on the sand to get positioned for the next wave to carry him back into the water.
On the beach, the other pups in the group emerged unscathed from the explosion of foam kicked up by the attack.
They were so close to us we could see their eyes. We were under strict instructions not to move and mess up the hunt. Any gesture or noise could distract them from the ocean, where the black fin of another orca loomed.
Having travelled far and waited for hours to see an attack, at first I mentally urged Mel on so we could get a good story.
But the little sea lions were cute, and I started to question my enthusiasm as Mel's killing continued.
The orcas, the oceans' fiercest predators, come to Punta Norte every March, staying up to 45 days and building up blubber on a diet of sea-lion pups.
The surviving sea lions are swimming well enough by the Southern Hemisphere winter to elude the killer whales.
Our visit was carefully orchestrated because experts fear human intervention could affect the hunt, perhaps permanently.
Only a few visitors - researchers, nature photographers and journalists - are allowed here each autumn, paying hundreds of dollars for the privilege, and escorted by specialists who control every movement as they record details of the hunt for research.
"Grounded with capture, grounded with capture," the ranger breathed into his two-way radio as Mel took the pup out to sea and shared it with another killer whale.
I stayed face down on the sand until the guide told me I could sit up for a bit to work out the cramps.
After the first attack, as petrels scavenged sea lion bits spat out by the orcas, Mel cruised up and down the coast again, turning 45º on his side to hide his 5ft (1.5-metre) high fin and watching for more unsteady pups.
For the next several hours only bigger sea lions crossed the channel area the orcas hunt in. Mel didn't bother pursuing the strong swimmers, but when the pups returned, the hunt started up again.
During the two days we spent on the beach, the magnificent animal, believed to be more than 40 years old, launched himself onto the sand 14 times and almost always got his pup. A smaller whale also made a few attempts but failed.
On the third day, the wind changed and the orcas didn't come into the channel, but experienced photographers who have spent several seasons watching the orcas said we had been lucky to witness a spectacular two days of hunting.