PORTE JOFRE, PANTANAL, BRAZILOn a particularly hot afternoon last October, two jaguar sisters named Medrosa and Jaju went down to the river to drink.

But before they had reached the waters of the Corixo Negro, a giant otter loudly voiced its displeasure.

A top predator, the river otter is known to some local people in Brazil's Pantanal as the "aquatic jaguar"—and indeed in this showdown, the otter's vocalizations and rapid movements sent the real big cats quickly backtracking. (Can you spot the difference between a jaguar and a leopard?)

"The sisters' mother, Patricia, is an excellent caiman hunter, but we have no record of her standing against giant otters," Rafael Hoogesteijn, jaguar program conflict director for the wildcat conservation group Panthera, wrote on their blog.

"So the young females may have feared the otter because of never seeing their mother face its kind before," says Hoogesteijn, who filmed the encounter.

The Element of Surprise

The two predators are such worthy foes, there's only one recorded case of a jaguar killing a giant otter.

In 2012, one of the big cats killed a radio-collared giant otter that was sleeping under a fallen tree trunk in the Brazilian Amazon. The fact the otter was isolated on land may have been a factor, the authors conclude in the study.

"Otters are very comfortable in the water, and they know that in the water they can escape jaguars," notes Esteban Payan, a National Geographic explorer and northern South America program director for Panthera. (Get seven surprising facts about giant otters.)

"In fact, the only way jaguars can catch otters is by using the element of surprise."

Ailton Lara, director of the Pantanal Jaguar Camp, has also observed that "otters are much faster than a jaguar when they are in the water."

A few weeks before the solo otter standoff, Lara saw a jaguar trying to catch a family of otters along the São Lourenço River. The otters made loud calls and started surrounding and splashing the jaguar, nicknamed Ague, in a show of intimidation (seen in the video above).

"Their tactics were working, you could tell by the way Ague was continuously flicking her tail that she was afraid," he says.

Bouncing Back

But why are jaguar and otter interactions so rarely seen?

For one, both species have been so heavily persecuted that in the past, there were simply fewer of them, Luke Hunter, Panthera's chief conservation officer, said by email.

This made "surviving jaguars and otters incredibly shy of people so that, even when such encounters occurred, there was almost no chance of them unfolding in view of human observers," Hunter says. (Read more about jaguars, the "sumo wrestlers" of the animal kingdom.)

"Today, that situation has been transformed" as conservationists work to increase the animals' numbers in the region.

The International Union for Conservation of Nature lists the jaguar as near-threatened by extinction across its range, although its population in the Pantanal remains stable. The giant otter is endangered, and the Pantanal is one of the few regions where it seems to be recovering.

Payan adds that South American tourists are not as accustomed to watching wildlife dramas unfold.

"You see so many interactions between, say, lions and hyenas in Africa," he says. "Well, this is similar stuff, but in South America, and I'm so excited that it has been captured."