Lilly King and Yulia Efimova's Olympic rivalry was never destined to stay confined to the pool at the Olympic Aquatics Stadium, not with King's sudden prominence as a doping vigilante.

Now, with the swimming events in Rio all finished, Russia's Efimova is opening up about the emotional toll of US swimmer King's outspokenness.

"It was war," Efimova told USA Today.

"It was like a nightmare. This completion is a relief because I love racing, but this was more like a war."