In Tuesday's free routine duet final at the Rio 2016 Olympics, they at least pretended to.
Wearing scale-inspired swimsuits and batting their legs out of the water, feet sticking out to look like tails, they collected gold - as expected - and came even closer to sealing their status as sirens.
"Sometimes everyone calls us mermaids and asks us if we have gills, so we are really comfortable in this performance," said Romashina after their routine, as she took bobby pins out of her heavily gelled-back hair.
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The Russians earned a final score of 194.9910, while China's pair pocketed silver with 192.3688 and Japan took bronze with 188.0547.
Russians, bringing a tradition of ballet to the pool, have taken home the Olympic gold for duets since Sydney in 2000, earning a reputation for extreme precision and ever more original routines.
The mermaid choreography was so special for the Russian pair, which also won gold at London 2012, that they had the enticing music specially written for the Games.
Ishchenko and Romashina said they would take a "short break" to think about whether to continue in the discipline. But they declined to shed light on how they came to dominate it.
"It's our secret!" joked Romashina.
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USA's Artistic Swimming performance at London 2012