noun
dangerous waters
Literal use for bodies of water that are hazardous for navigation, swimming, etc.
この海域は危険水域に指定されている。
This sea area is designated as dangerous waters.
noun
dangerous stretch; risky area
Figurative use for a situation, economy, or condition that has entered a critical or precarious phase.
景気は危険水域に入ったと専門家は警告している。
Experts warn that the economy has entered a dangerous stretch.
彼の血圧は危険水域に達している。
His blood pressure has reached a risky area.