3 sentences for 警戒线 (jǐng​jiè​xiàn — alert level)

1. 水位降到了警戒线以下。

   shuǐ​wèi jiàng​dào le jǐng​jiè​xiàn yǐ​xià.

   The water level has dropped below the warning line.

   Source: Dong Chinese Dictionary

2. 河水的水位已经超过了安全警戒线。

   hé​shuǐ de shuǐ​wèi yǐ​jīng chāo​guò le ān​quán jǐng​jiè​xiàn.

   The river level has exceeded the safety warning line.

   Source: Dong Chinese Dictionary

3. 由于持续干旱，水库的水量已经降到了警戒线以下。

   yóu​yú chí​xù gān​hàn, shuǐ​kù de shuǐ​liàng yǐ​jīng jiàng​dào le jǐng​jiè​xiàn yǐ​xià.

   Due to the ongoing drought, the water level in the reservoir has dropped below the warning line.

   Source: Dong Chinese Dictionary