Word: 水底 (shuǐdǐ)

水底下推船，卖力看不见

shuǐdǐ xia tuī chuán, màilì kànbújiàn

pushing a boat underwater: the effort can't be seen

湖水清澈，能看见水底的石头。

Hú shuǐ qīngchè, néng kànjiàn shuǐdǐ de shítou.

The lake water is so clear that you can see the stones on the bottom.

空中的雁,水底的鱼,想抓抓不着

kōngzhōng de yàn,shuǐdǐ de yú,xiǎng zhuā zhuā bù zháo

geese in the sky, fish at the bottom of the water: you want to catch them but can't