Meaning:
Literally meaning paddle on a calm body of water or make strokes with one’s arms, this internet catchphrase are now used to describe people who work less hard than one usually should do.
The word was first used to describe lazy boatmen who would half-heartedly splash their oars from side to side while their colleagues did the actual rowing. However people then gradually expand the meaning to cover more people.
Similar expressions include slack off, loaf on the job and even goof off.
Example:
A: 上周综艺节目里，我最喜爱的唱歌组合被淘汰了，太让我难过了。
Shàngzhōu zōngyì jiémù lǐ, wǒ zuì xǐài de chànggē zǔhé bèi táotài le，tài ràngwǒ nánguò le。
My favorite vocal team was eliminated in the last round of the competition. I feel so sad about it.
B: 那个女团成员舞蹈动作都忘了，明显是在划水。
Nàgè nǚtuán chéngyuán wǔdǎo dòngzuò dōu wàng le，míngxiǎn shì zài huáshuǐ。
That band member forgot all her dance moves. She is definitely slacking.