low-water mark

noun

A mark, such as a line of seaweed, showing the lowest level reached by a body of water. / (by extension) The nadir or lowest point of something.

The low-water mark on the river indicates the lowest point the water level has reached.

意味（1）

A mark, such as a line of seaweed, showing the lowest level reached by a body of water.

意味（2）

(by extension) The nadir or lowest point of something.