中流

zhōng liú shuǐ hěn jí

中流水很急。

There's a fast current in midstream.

zhōng liú dǐ zhù

中流砥柱

firm rock in midstream - mainstay

chǔ yú zhōng liú shuǐ píng

处于中流水平

be of middling level

shēn chǔ zhōng liú shè huì

身处中流社会

be in the middle stratum society